systemd.exec(5) - Man pages

SYSTEMD.EXEC(5) systemd.exec SYSTEMD.EXEC(5)

NAME
systemd.exec - Execution environment configuration

SYNOPSIS
service.service, socket.socket, mount.mount, swap.swap

DESCRIPTION
Unit configuration files for services, sockets, mount points, and swap
devices share a subset of configuration options which define the
execution environment of spawned processes.

This man page lists the configuration options shared by these four unit
types. See systemd.unit(5) for the common options of all unit
configuration files, and systemd.service(5), systemd.socket(5),
systemd.swap(5), and systemd.mount(5) for more information on the
specific unit configuration files. The execution specific configuration
options are configured in the [Service], [Socket], [Mount], or [Swap]
sections, depending on the unit type.

In addition, options which control resources through Linux Control
Groups (cgroups) are listed in systemd.resource-control(5). Those
options complement options listed here.

IMPLICIT DEPENDENCIES
A few execution parameters result in additional, automatic dependencies
to be added:

• Units with WorkingDirectory=, RootDirectory=, RootImage=,
RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=
or ConfigurationDirectory= set automatically gain dependencies of
type Requires= and After= on all mount units required to access the
specified paths. This is equivalent to having them listed explicitly
in RequiresMountsFor=.

• Similarly, units with PrivateTmp= enabled automatically get mount
unit dependencies for all mounts required to access /tmp/ and
/var/tmp/. They will also gain an automatic After= dependency on
systemd-tmpfiles-setup.service(8).

• Units whose standard output or error output is connected to journal
or kmsg (or their combinations with console output, see below)
automatically acquire dependencies of type After= on
systemd-journald.socket.

• Units using LogNamespace= will automatically gain ordering and
requirement dependencies on the two socket units associated with
systemd-journald@.service instances.

PATHS
The following settings may be used to change a service's view of the
filesystem. Please note that the paths must be absolute and must not
contain a ".." path component.

ExecSearchPath=
Takes a colon separated list of absolute paths relative to which the
executable used by the Exec*= (e.g. ExecStart=, ExecStop=, etc.)
properties can be found. ExecSearchPath= overrides $PATH if $PATH
is not supplied by the user through Environment=, EnvironmentFile=
or PassEnvironment=. Assigning an empty string removes previous
assignments and setting ExecSearchPath= to a value multiple times
will append to the previous setting.

Added in version 250.

WorkingDirectory=
Takes a directory path relative to the service's root directory
specified by RootDirectory=, or the special value "~". Sets the
working directory for executed processes. If set to "~", the home
directory of the user specified in User= is used. If not set,
defaults to the root directory when systemd is running as a system
instance and the respective user's home directory if run as user. If
the setting is prefixed with the "-" character, a missing working
directory is not considered fatal. If RootDirectory=/RootImage= is
not set, then WorkingDirectory= is relative to the root of the
system running the service manager. Note that setting this parameter
might result in additional dependencies to be added to the unit (see
above).

RootDirectory=
Takes a directory path relative to the host's root directory (i.e.
the root of the system running the service manager). Sets the root
directory for executed processes, with the pivot_root(2) or
chroot(2) system call. If this is used, it must be ensured that the
process binary and all its auxiliary files are available in the new
root. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).

The MountAPIVFS= and PrivateUsers= settings are particularly useful
in conjunction with RootDirectory=. For details, see below.

If RootDirectory=/RootImage= are used together with NotifyAccess=
the notification socket is automatically mounted from the host into
the root environment, to ensure the notification interface can work
correctly.

Note that services using RootDirectory=/RootImage= will not be able
to log via the syslog or journal protocols to the host logging
infrastructure, unless the relevant sockets are mounted from the
host, specifically:

The host's os-release(5) file will be made available for the service
(read-only) as /run/host/os-release. It will be updated
automatically on soft reboot (see: systemd-soft-reboot.service(8)),
in case the service is configured to survive it.

Example 1. Mounting logging sockets into root environment

BindReadOnlyPaths=/dev/log /run/systemd/journal/socket /run/systemd/journal/stdout

In place of the directory path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.

This option is only available for system services, or for services
running in per-user instances of the service manager in which case
PrivateUsers= is implicitly enabled (requires unprivileged user
namespaces support to be enabled in the kernel via the
"kernel.unprivileged_userns_clone=" sysctl).

RootImage=
Takes a path to a block device node or regular file as argument.
This call is similar to RootDirectory= however mounts a file system
hierarchy from a block device node or loopback file instead of a
directory. The device node or file system image file needs to
contain a file system without a partition table, or a file system
within an MBR/MS-DOS or GPT partition table with only a single
Linux-compatible partition, or a set of file systems within a GPT
partition table that follows the Discoverable Partitions
Specification[1].

When DevicePolicy= is set to "closed" or "strict", or set to "auto"
and DeviceAllow= is set, then this setting adds /dev/loop-control
with rw mode, "block-loop" and "block-blkext" with rwm mode to
DeviceAllow=. See systemd.resource-control(5) for the details about
DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as
it may change the setting of DevicePolicy=.

Units making use of RootImage= automatically gain an After=
dependency on systemd-udevd.service.

In place of the image path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 233.

RootImageOptions=
Takes a comma-separated list of mount options that will be used on
disk images specified by RootImage=. Optionally a partition name can
be prefixed, followed by colon, in case the image has multiple
partitions, otherwise partition name "root" is implied. Options for
multiple partitions can be specified in a single line with space
separators. Assigning an empty string removes previous assignments.
Duplicated options are ignored. For a list of valid mount options,
please refer to mount(8).

Valid partition names follow the Discoverable Partitions
Specification[1]: root, usr, home, srv, esp, xbootldr, tmp, var.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 247.

RootEphemeral=
Takes a boolean argument. If enabled, executed processes will run in
an ephemeral copy of the root directory or root image. The ephemeral
copy is placed in /var/lib/systemd/ephemeral-trees/ while the
service is active and is cleaned up when the service is stopped or
restarted. If RootDirectory= is used and the root directory is a
subvolume, the ephemeral copy will be created by making a snapshot
of the subvolume.

To make sure making ephemeral copies can be made efficiently, the
root directory or root image should be located on the same
filesystem as /var/lib/systemd/ephemeral-trees/. When using
RootEphemeral= with root directories, btrfs(5) should be used as the
filesystem and the root directory should ideally be a subvolume
which systemd can snapshot to make the ephemeral copy. For root
images, a filesystem with support for reflinks should be used to
ensure an efficient ephemeral copy.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 254.

RootHash=
Takes a data integrity (dm-verity) root hash specified in
hexadecimal, or the path to a file containing a root hash in ASCII
hexadecimal format. This option enables data integrity checks using
dm-verity, if the used image contains the appropriate integrity data
(see above) or if RootVerity= is used. The specified hash must match
the root hash of integrity data, and is usually at least 256 bits
(and hence 64 formatted hexadecimal characters) long (in case of
SHA256 for example). If this option is not specified, but the image
file carries the "user.verity.roothash" extended file attribute (see
xattr(7)), then the root hash is read from it, also as formatted
hexadecimal characters. If the extended file attribute is not found
(or is not supported by the underlying file system), but a file with
the .roothash suffix is found next to the image file, bearing
otherwise the same name (except if the image has the .raw suffix, in
which case the root hash file must not have it in its name), the
root hash is read from it and automatically used, also as formatted
hexadecimal characters.

If the disk image contains a separate /usr/ partition it may also be
Verity protected, in which case the root hash may configured via an
extended attribute "user.verity.usrhash" or a .usrhash file adjacent
to the disk image. There's currently no option to configure the root
hash for the /usr/ file system via the unit file directly.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 246.

RootHashSignature=
Takes a PKCS7 signature of the RootHash= option as a path to a
DER-encoded signature file, or as an ASCII base64 string encoding of
a DER-encoded signature prefixed by "base64:". The dm-verity volume
will only be opened if the signature of the root hash is valid and
signed by a public key present in the kernel keyring. If this option
is not specified, but a file with the .roothash.p7s suffix is found
next to the image file, bearing otherwise the same name (except if
the image has the .raw suffix, in which case the signature file must
not have it in its name), the signature is read from it and
automatically used.

If the disk image contains a separate /usr/ partition it may also be
Verity protected, in which case the signature for the root hash may
configured via a .usrhash.p7s file adjacent to the disk image.
There's currently no option to configure the root hash signature for
the /usr/ via the unit file directly.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 246.

RootVerity=
Takes the path to a data integrity (dm-verity) file. This option
enables data integrity checks using dm-verity, if RootImage= is used
and a root-hash is passed and if the used image itself does not
contain the integrity data. The integrity data must be matched by
the root hash. If this option is not specified, but a file with the
.verity suffix is found next to the image file, bearing otherwise
the same name (except if the image has the .raw suffix, in which
case the verity data file must not have it in its name), the verity
data is read from it and automatically used.

This option is supported only for disk images that contain a single
file system, without an enveloping partition table. Images that
contain a GPT partition table should instead include both root file
system and matching Verity data in the same image, implementing the
Discoverable Partitions Specification[1].

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 246.

RootImagePolicy=, MountImagePolicy=, ExtensionImagePolicy=
Takes an image policy string as per systemd.image-policy(7) to use
when mounting the disk images (DDI) specified in RootImage=,
MountImage=, ExtensionImage=, respectively. If not specified the
following policy string is the default for RootImagePolicy= and
MountImagePolicy:

root=verity+signed+encrypted+unprotected+absent: \
usr=verity+signed+encrypted+unprotected+absent: \
home=encrypted+unprotected+absent: \
srv=encrypted+unprotected+absent: \
tmp=encrypted+unprotected+absent: \
var=encrypted+unprotected+absent

The default policy for ExtensionImagePolicy= is:

root=verity+signed+encrypted+unprotected+absent: \
usr=verity+signed+encrypted+unprotected+absent

Added in version 254.

MountAPIVFS=
Takes a boolean argument. If on, a private mount namespace for the
unit's processes is created and the API file systems /proc/, /sys/,
/dev/ and /run/ (as an empty "tmpfs") are mounted inside of it,
unless they are already mounted. Note that this option has no effect
unless used in conjunction with RootDirectory=/RootImage= as these
four mounts are generally mounted in the host anyway, and unless the
root directory is changed, the private mount namespace will be a 1:1
copy of the host's, and include these four mounts. Note that the
/dev/ file system of the host is bind mounted if this option is used
without PrivateDevices=. To run the service with a private, minimal
version of /dev/, combine this option with PrivateDevices=.

In order to allow propagating mounts at runtime in a safe manner,
/run/systemd/propagate/ on the host will be used to set up new
mounts, and /run/host/incoming/ in the private namespace will be
used as an intermediate step to store them before being moved to the
final mount point.

Added in version 233.

BindLogSockets=
Takes a boolean argument. If true, sockets from systemd-
journald.socket(8) will be bind mounted into the mount namespace.
This is particularly useful when a different instance of /run/ is
employed, to make sure processes running in the namespace can still
make use of sd-journal(3).

This option is implied when LogNamespace= is used, when
MountAPIVFS=yes, or when PrivateDevices=yes is used in conjunction
with either RootDirectory= or RootImage=.

Added in version 257.

ProtectProc=
Takes one of "noaccess", "invisible", "ptraceable" or "default"
(which it defaults to). When set, this controls the "hidepid=" mount
option of the "procfs" instance for the unit that controls which
directories with process metainformation (/proc/PID) are visible and
accessible: when set to "noaccess" the ability to access most of
other users' process metadata in /proc/ is taken away for processes
of the service. When set to "invisible" processes owned by other
users are hidden from /proc/. If "ptraceable" all processes that
cannot be ptrace()'ed by a process are hidden to it. If "default" no
restrictions on /proc/ access or visibility are made. For further
details see The /proc Filesystem[2]. It is generally recommended to
run most system services with this option set to "invisible". This
option is implemented via file system namespacing, and thus cannot
be used with services that shall be able to install mount points in
the host file system hierarchy. Note that the root user is
unaffected by this option, so to be effective it has to be used
together with User= or DynamicUser=yes, and also without the
"CAP_SYS_PTRACE" capability, which also allows a process to bypass
this feature. It cannot be used for services that need to access
metainformation about other users' processes. This option implies
MountAPIVFS=.

If the kernel does not support per-mount point hidepid= mount
options this setting remains without effect, and the unit's
processes will be able to access and see other process as if the
option was not used.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 247.

ProcSubset=
Takes one of "all" (the default) and "pid". If "pid", all files and
directories not directly associated with process management and
introspection are made invisible in the /proc/ file system
configured for the unit's processes. This controls the "subset="
mount option of the "procfs" instance for the unit. For further
details see The /proc Filesystem[2]. Note that Linux exposes various
kernel APIs via /proc/, which are made unavailable with this
setting. Since these APIs are used frequently this option is useful
only in a few, specific cases, and is not suitable for most
non-trivial programs.

Much like ProtectProc= above, this is implemented via file system
mount namespacing, and hence the same restrictions apply: it is only
available to system services, it disables mount propagation to the
host mount table, and it implies MountAPIVFS=. Also, like
ProtectProc= this setting is gracefully disabled if the used kernel
does not support the "subset=" mount option of "procfs".

Added in version 247.

BindPaths=, BindReadOnlyPaths=
Configures unit-specific bind mounts. A bind mount makes a
particular file or directory available at an additional place in the
unit's view of the file system. Any bind mounts created with this
option are specific to the unit, and are not visible in the host's
mount table. This option expects a whitespace separated list of bind
mount definitions. Each definition consists of a colon-separated
triple of source path, destination path and option string, where the
latter two are optional. If only a source path is specified the
source and destination is taken to be the same. The option string
may be either "rbind" or "norbind" for configuring a recursive or
non-recursive bind mount. If the destination path is omitted, the
option string must be omitted too. Each bind mount definition may be
prefixed with "-", in which case it will be ignored when its source
path does not exist.

BindPaths= creates regular writable bind mounts (unless the source
file system mount is already marked read-only), while
BindReadOnlyPaths= creates read-only bind mounts. These settings may
be used more than once, each usage appends to the unit's list of
bind mounts. If the empty string is assigned to either of these two
options the entire list of bind mounts defined prior to this is
reset. Note that in this case both read-only and regular bind mounts
are reset, regardless which of the two settings is used.

Using this option implies that a mount namespace is allocated for
the unit, i.e. it implies the effect of PrivateMounts= (see below).

This option is particularly useful when RootDirectory=/RootImage= is
used. In this case the source path refers to a path on the host file
system, while the destination path refers to a path below the root
directory of the unit.

Note that the destination directory must exist or systemd must be
able to create it. Thus, it is not possible to use those options for
mount points nested underneath paths specified in
InaccessiblePaths=, or under /home/ and other protected directories
if ProtectHome=yes is specified. TemporaryFileSystem= with ":ro" or
ProtectHome=tmpfs should be used instead.

Added in version 233.

MountImages=
This setting is similar to RootImage= in that it mounts a file
system hierarchy from a block device node or loopback file, but the
destination directory can be specified as well as mount options.
This option expects a whitespace separated list of mount
definitions. Each definition consists of a colon-separated tuple of
source path and destination definitions, optionally followed by
another colon and a list of mount options.

Mount options may be defined as a single comma-separated list of
options, in which case they will be implicitly applied to the root
partition on the image, or a series of colon-separated tuples of
partition name and mount options. Valid partition names and mount
options are the same as for RootImageOptions= setting described
above.

Each mount definition may be prefixed with "-", in which case it
will be ignored when its source path does not exist. The source
argument is a path to a block device node or regular file. If source
or destination contain a ":", it needs to be escaped as "\:". The
device node or file system image file needs to follow the same rules
as specified for RootImage=. Any mounts created with this option are
specific to the unit, and are not visible in the host's mount table.

These settings may be used more than once, each usage appends to the
unit's list of mount paths. If the empty string is assigned, the
entire list of mount paths defined prior to this is reset.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 247.

ExtensionImages=
This setting is similar to MountImages= in that it mounts a file
system hierarchy from a block device node or loopback file, but
instead of providing a destination path, an overlay will be set up.
This option expects a whitespace separated list of mount
definitions. Each definition consists of a source path, optionally
followed by a colon and a list of mount options.

A read-only OverlayFS will be set up on top of /usr/ and /opt/
hierarchies for sysext images and /etc/ hierarchy for confext
images. The order in which the images are listed will determine the
order in which the overlay is laid down: images specified first to
last will result in overlayfs layers bottom to top.

Each mount definition may be prefixed with "-", in which case it
will be ignored when its source path does not exist. The source
argument is a path to a block device node or regular file. If the
source path contains a ":", it needs to be escaped as "\:". The
device node or file system image file needs to follow the same rules
as specified for RootImage=. Any mounts created with this option are
specific to the unit, and are not visible in the host's mount table.

These settings may be used more than once, each usage appends to the
unit's list of image paths. If the empty string is assigned, the
entire list of mount paths defined prior to this is reset.

Each sysext image must carry a
/usr/lib/extension-release.d/extension-release.IMAGE file while each
confext image must carry a
/etc/extension-release.d/extension-release.IMAGE file, with the
appropriate metadata which matches RootImage=/RootDirectory= or the
host. See: os-release(5). To disable the safety check that the
extension-release file name matches the image file name, the
x-systemd.relax-extension-release-check mount option may be
appended.

In place of the image path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 248.

ExtensionDirectories=
This setting is similar to BindReadOnlyPaths= in that it mounts a
file system hierarchy from a directory, but instead of providing a
destination path, an overlay will be set up. This option expects a
whitespace separated list of source directories.

A read-only OverlayFS will be set up on top of /usr/ and /opt/
hierarchies for sysext images and /etc/ hierarchy for confext
images. The order in which the directories are listed will determine
the order in which the overlay is laid down: directories specified
first to last will result in overlayfs layers bottom to top.

Each directory listed in ExtensionDirectories= may be prefixed with
"-", in which case it will be ignored when its source path does not
exist. Any mounts created with this option are specific to the unit,
and are not visible in the host's mount table.

These settings may be used more than once, each usage appends to the
unit's list of directories paths. If the empty string is assigned,
the entire list of mount paths defined prior to this is reset.

Each sysext directory must contain a
/usr/lib/extension-release.d/extension-release.IMAGE file while each
confext directory must carry a
/etc/extension-release.d/extension-release.IMAGE file, with the
appropriate metadata which matches RootImage=/RootDirectory= or the
host. See: os-release(5).

Note that usage from user units requires overlayfs support in
unprivileged user namespaces, which was first introduced in kernel
v5.11.

In place of the directory path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.

Added in version 251.

USER/GROUP IDENTITY
These options are only available for system services and are not
supported for services running in per-user instances of the service
manager.

User=, Group=
Set the UNIX user or group that the processes are executed as,
respectively. Takes a single user or group name, or a numeric ID as
argument. For system services (services run by the system service
manager, i.e. managed by PID 1) and for user services of the root
user (services managed by root's instance of systemd --user), the
default is "root", but User= may be used to specify a different
user. For user services of any other user, switching user identity
is not permitted, hence the only valid setting is the same user the
user's service manager is running as. If no group is set, the
default group of the user is used. This setting does not affect
commands whose command line is prefixed with "+".

Note that this enforces only weak restrictions on the user/group
name syntax, but will generate warnings in many cases where
user/group names do not adhere to the following rules: the specified
name should consist only of the characters a-z, A-Z, 0-9, "_" and
"-", except for the first character which must be one of a-z, A-Z
and "_" (i.e. digits and "-" are not permitted as first character).
The user/group name must have at least one character, and at most
31. These restrictions are made in order to avoid ambiguities and to
ensure user/group names and unit files remain portable among Linux
systems. For further details on the names accepted and the names
warned about see User/Group Name Syntax[3].

When used in conjunction with DynamicUser= the user/group name
specified is dynamically allocated at the time the service is
started, and released at the time the service is stopped — unless it
is already allocated statically (see below). If DynamicUser= is not
used the specified user and group must have been created statically
in the user database no later than the moment the service is
started, for example using the sysusers.d(5) facility, which is
applied at boot or package install time. If the user does not exist
by then program invocation will fail.

If the User= setting is used the supplementary group list is
initialized from the specified user's default group list, as defined
in the system's user and group database. Additional groups may be
configured through the SupplementaryGroups= setting (see below).

DynamicUser=
Takes a boolean parameter. If set, a UNIX user and group pair is
allocated dynamically when the unit is started, and released as soon
as it is stopped. The user and group will not be added to
/etc/passwd or /etc/group, but are managed transiently during
runtime. The nss-systemd(8) glibc NSS module provides integration of
these dynamic users/groups into the system's user and group
databases. The user and group name to use may be configured via
User= and Group= (see above). If these options are not used and
dynamic user/group allocation is enabled for a unit, the name of the
dynamic user/group is implicitly derived from the unit name. If the
unit name without the type suffix qualifies as valid user name it is
used directly, otherwise a name incorporating a hash of it is used.
If a statically allocated user or group of the configured name
already exists, it is used and no dynamic user/group is allocated.
Note that if User= is specified and the static group with the name
exists, then it is required that the static user with the name
already exists. Similarly, if Group= is specified and the static
user with the name exists, then it is required that the static group
with the name already exists. Dynamic users/groups are allocated
from the UID/GID range 61184...65519. It is recommended to avoid
this range for regular system or login users. At any point in time
each UID/GID from this range is only assigned to zero or one
dynamically allocated users/groups in use. However, UID/GIDs are
recycled after a unit is terminated. Care should be taken that any
processes running as part of a unit for which dynamic users/groups
are enabled do not leave files or directories owned by these
users/groups around, as a different unit might get the same UID/GID
assigned later on, and thus gain access to these files or
directories. If DynamicUser= is enabled, RemoveIPC= is implied (and
cannot be turned off). This ensures that the lifetime of IPC objects
and temporary files created by the executed processes is bound to
the runtime of the service, and hence the lifetime of the dynamic
user/group. Since /tmp/ and /var/tmp/ are usually the only
world-writable directories on a system, unless PrivateTmp= is
manually set to "true", "disconnected" would be implied. This
ensures that a unit making use of dynamic user/group allocation
cannot leave files around after unit termination. Furthermore
NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled (and
cannot be disabled), to ensure that processes invoked cannot take
benefit or create SUID/SGID files or directories. Moreover
ProtectSystem=strict and ProtectHome=read-only are implied, thus
prohibiting the service to write to arbitrary file system locations.
In order to allow the service to write to certain directories, they
have to be allow-listed using ReadWritePaths=, but care must be
taken so that UID/GID recycling does not create security issues
involving files created by the service. Use RuntimeDirectory= (see
below) in order to assign a writable runtime directory to a service,
owned by the dynamic user/group and removed automatically when the
unit is terminated. Use StateDirectory=, CacheDirectory= and
LogsDirectory= in order to assign a set of writable directories for
specific purposes to the service in a way that they are protected
from vulnerabilities due to UID reuse (see below). If this option is
enabled, care should be taken that the unit's processes do not get
access to directories outside of these explicitly configured and
managed ones. Specifically, do not use BindPaths= and be careful
with AF_UNIX file descriptor passing for directory file descriptors,
as this would permit processes to create files or directories owned
by the dynamic user/group that are not subject to the lifecycle and
access guarantees of the service. Note that this option is currently
incompatible with D-Bus policies, thus a service using this option
may currently not allocate a D-Bus service name (note that this does
not affect calling into other D-Bus services). Defaults to off.

Added in version 232.

SupplementaryGroups=
Sets the supplementary Unix groups the processes are executed as.
This takes a space-separated list of group names or IDs. This option
may be specified more than once, in which case all listed groups are
set as supplementary groups. When the empty string is assigned, the
list of supplementary groups is reset, and all assignments prior to
this one will have no effect. In any way, this option does not
override, but extends the list of supplementary groups configured in
the system group database for the user. This does not affect
commands prefixed with "+".

SetLoginEnvironment=
Takes a boolean parameter that controls whether to set the $HOME,
$LOGNAME, and $SHELL environment variables. If not set, this
defaults to true if User=, DynamicUser= or PAMName= are set, false
otherwise. If set to true, the variables will always be set for
system services, i.e. even when the default user "root" is used. If
set to false, the mentioned variables are not set by the service
manager, no matter whether User=, DynamicUser=, or PAMName= are used
or not. This option normally has no effect on services of the
per-user service manager, since in that case these variables are
typically inherited from user manager's own environment anyway.

Added in version 255.

PAMName=
Sets the PAM service name to set up a session as. If set, the
executed process will be registered as a PAM session under the
specified service name. This is only useful in conjunction with the
User= setting, and is otherwise ignored. If not set, no PAM session
will be opened for the executed processes. See pam(8) for details.

Note that for each unit making use of this option a PAM session
handler process will be maintained as part of the unit and stays
around as long as the unit is active, to ensure that appropriate
actions can be taken when the unit and hence the PAM session
terminates. This process is named "(sd-pam)" and is an immediate
child process of the unit's main process.

Note that when this option is used for a unit it is very likely
(depending on PAM configuration) that the main unit process will be
migrated to its own session scope unit when it is activated. This
process will hence be associated with two units: the unit it was
originally started from (and for which PAMName= was configured), and
the session scope unit. Any child processes of that process will
however be associated with the session scope unit only. This has
implications when used in combination with NotifyAccess=all, as
these child processes will not be able to affect changes in the
original unit through notification messages. These messages will be
considered belonging to the session scope unit and not the original
unit. It is hence not recommended to use PAMName= in combination
with NotifyAccess=all.

CAPABILITIES
These options are only available for system services, or for services
running in per-user instances of the service manager in which case
PrivateUsers= is implicitly enabled (requires unprivileged user
namespaces support to be enabled in the kernel via the
"kernel.unprivileged_userns_clone=" sysctl).

CapabilityBoundingSet=
Controls which capabilities to include in the capability bounding
set for the executed process. See capabilities(7) for details. Takes
a whitespace-separated list of capability names, e.g.
CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities listed
will be included in the bounding set, all others are removed. If the
list of capabilities is prefixed with "~", all but the listed
capabilities will be included, the effect of the assignment
inverted. Note that this option also affects the respective
capabilities in the effective, permitted and inheritable capability
sets. If this option is not used, the capability bounding set is not
modified on process execution, hence no limits on the capabilities
of the process are enforced. This option may appear more than once,
in which case the bounding sets are merged by OR, or by AND if the
lines are prefixed with "~" (see below). If the empty string is
assigned to this option, the bounding set is reset to the empty
capability set, and all prior settings have no effect. If set to "~"
(without any further argument), the bounding set is reset to the
full set of available capabilities, also undoing any previous
settings. This does not affect commands prefixed with "+".

Use systemd-analyze(1)'s capability command to retrieve a list of
capabilities defined on the local system.

Example: if a unit has the following,

CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=CAP_B CAP_C

then CAP_A, CAP_B, and CAP_C are set. If the second line is prefixed
with "~", e.g.,

CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=~CAP_B CAP_C

then, only CAP_A is set.

AmbientCapabilities=
Controls which capabilities to include in the ambient capability set
for the executed process. Takes a whitespace-separated list of
capability names, e.g. CAP_SYS_ADMIN, CAP_DAC_OVERRIDE,
CAP_SYS_PTRACE. This option may appear more than once, in which case
the ambient capability sets are merged (see the above examples in
CapabilityBoundingSet=). If the list of capabilities is prefixed
with "~", all but the listed capabilities will be included, the
effect of the assignment inverted. If the empty string is assigned
to this option, the ambient capability set is reset to the empty
capability set, and all prior settings have no effect. If set to "~"
(without any further argument), the ambient capability set is reset
to the full set of available capabilities, also undoing any previous
settings. Note that adding capabilities to the ambient capability
set adds them to the process's inherited capability set.

Ambient capability sets are useful if you want to execute a process
as a non-privileged user but still want to give it some
capabilities. Note that in this case option keep-caps is
automatically added to SecureBits= to retain the capabilities over
the user change. AmbientCapabilities= does not affect commands
prefixed with "+".

Added in version 229.

SECURITY
NoNewPrivileges=
Takes a boolean argument. If true, ensures that the service process
and all its children can never gain new privileges through execve()
(e.g. via setuid or setgid bits, or filesystem capabilities). This
is the simplest and most effective way to ensure that a process and
its children can never elevate privileges again. Defaults to false.
In case the service will be run in a new mount namespace anyway and
SELinux is disabled, all file systems are mounted with MS_NOSUID
flag. Also see No New Privileges Flag[4].

Note that this setting only has an effect on the unit's processes
themselves (or any processes directly or indirectly forked off
them). It has no effect on processes potentially invoked on request
of them through tools such as at(1), crontab(1), systemd-run(1), or
arbitrary IPC services.

Added in version 187.

SecureBits=
Controls the secure bits set for the executed process. Takes a
space-separated combination of options from the following list:
keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot, and noroot-locked. This option may
appear more than once, in which case the secure bits are ORed. If
the empty string is assigned to this option, the bits are reset to
0. This does not affect commands prefixed with "+". See
capabilities(7) for details.

MANDATORY ACCESS CONTROL
SELinuxContext=
Set the SELinux security context of the executed process. If set,
this will override the automated domain transition. However, the
policy still needs to authorize the transition. This directive is
ignored if SELinux is disabled. If prefixed by "-", failing to set
the SELinux security context will be ignored, but it is still
possible that the subsequent execve() may fail if the policy does
not allow the transition for the non-overridden context. This does
not affect commands prefixed with "+". See setexeccon(3) for
details.

Added in version 209.

AppArmorProfile=
Takes a profile name as argument. The process executed by the unit
will switch to this profile when started. Profiles must already be
loaded in the kernel, or the unit will fail. If prefixed by "-", all
errors will be ignored. This setting has no effect if AppArmor is
not enabled. This setting does not affect commands prefixed with
"+".

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 210.

SmackProcessLabel=
Takes a SMACK64 security label as argument. The process executed by
the unit will be started under this label and SMACK will decide
whether the process is allowed to run or not, based on it. The
process will continue to run under the label specified here unless
the executable has its own SMACK64EXEC label, in which case the
process will transition to run under that label. When not specified,
the label that systemd is running under is used. This directive is
ignored if SMACK is disabled.

The value may be prefixed by "-", in which case all errors will be
ignored. An empty value may be specified to unset previous
assignments. This does not affect commands prefixed with "+".

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 218.

PROCESS PROPERTIES
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=,
LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=,
LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=, LimitRTTIME=
Set soft and hard limits on various resources for executed
processes. See setrlimit(2) for details on the process resource
limit concept. Process resource limits may be specified in two
formats: either as single value to set a specific soft and hard
limit to the same value, or as colon-separated pair soft:hard to set
both limits individually (e.g. "LimitAS=4G:16G"). Use the string
infinity to configure no limit on a specific resource. The
multiplicative suffixes K, M, G, T, P and E (to the base 1024) may
be used for resource limits measured in bytes (e.g. "LimitAS=16G").
For the limits referring to time values, the usual time units ms, s,
min, h and so on may be used (see systemd.time(7) for details). Note
that if no time unit is specified for LimitCPU= the default unit of
seconds is implied, while for LimitRTTIME= the default unit of
microseconds is implied. Also, note that the effective granularity
of the limits might influence their enforcement. For example, time
limits specified for LimitCPU= will be rounded up implicitly to
multiples of 1s. For LimitNICE= the value may be specified in two
syntaxes: if prefixed with "+" or "-", the value is understood as
regular Linux nice value in the range -20...19. If not prefixed like
this the value is understood as raw resource limit parameter in the
range 0...40 (with 0 being equivalent to 1).

Note that most process resource limits configured with these options
are per-process, and processes may fork in order to acquire a new
set of resources that are accounted independently of the original
process, and may thus escape limits set. Also note that LimitRSS= is
not implemented on Linux, and setting it has no effect. Often it is
advisable to prefer the resource controls listed in
systemd.resource-control(5) over these per-process limits, as they
apply to services as a whole, may be altered dynamically at runtime,
and are generally more expressive. For example, MemoryMax= is a more
powerful (and working) replacement for LimitRSS=.

Note that LimitNPROC= will limit the number of processes from one
(real) UID and not the number of processes started (forked) by the
service. Therefore the limit is cumulative for all processes running
under the same UID. Please also note that the LimitNPROC= will not
be enforced if the service is running as root (and not dropping
privileges). Due to these limitations, TasksMax= (see
systemd.resource-control(5)) is typically a better choice than
LimitNPROC=.

Resource limits not configured explicitly for a unit default to the
value configured in the various DefaultLimitCPU=,
DefaultLimitFSIZE=, ... options available in systemd-system.conf(5),
and – if not configured there – the kernel or per-user defaults, as
defined by the OS (the latter only for user services, see below).

For system units these resource limits may be chosen freely. When
these settings are configured in a user service (i.e. a service run
by the per-user instance of the service manager) they cannot be used
to raise the limits above those set for the user manager itself when
it was first invoked, as the user's service manager generally lacks
the privileges to do so. In user context these configuration options
are hence only useful to lower the limits passed in or to raise the
soft limit to the maximum of the hard limit as configured for the
user. To raise the user's limits further, the available
configuration mechanisms differ between operating systems, but
typically require privileges. In most cases it is possible to
configure higher per-user resource limits via PAM or by setting
limits on the system service encapsulating the user's service
manager, i.e. the user's instance of user@.service. After making
such changes, make sure to restart the user's service manager.

Table 1. Resource limit directives, their equivalent ulimit shell
commands and the unit used
┌──────────────────┬────────────┬──────────────────┬───────────────────┐
│ Directive │ ulimit │ Unit │ Notes │
│ │ equivalent │ │ │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitCPU= │ ulimit -t │ Seconds │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitFSIZE= │ ulimit -f │ Bytes │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitDATA= │ ulimit -d │ Bytes │ Do not use. This │
│ │ │ │ limits the │
│ │ │ │ allowed address │
│ │ │ │ range, not │
│ │ │ │ memory use! │
│ │ │ │ Defaults to │
│ │ │ │ unlimited and │
│ │ │ │ should not be │
│ │ │ │ lowered. To │
│ │ │ │ limit memory │
│ │ │ │ use, see │
│ │ │ │ MemoryMax= in │
│ │ │ │ systemd.resource- │
│ │ │ │ control(5). │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitSTACK= │ ulimit -s │ Bytes │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitCORE= │ ulimit -c │ Bytes │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitRSS= │ ulimit -m │ Bytes │ Do not use. No │
│ │ │ │ effect on Linux. │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitNOFILE= │ ulimit -n │ Number of File │ Do not use. Be │
│ │ │ Descriptors │ careful when │
│ │ │ │ raising the soft │
│ │ │ │ limit above 1024, │
│ │ │ │ since select(2) │
│ │ │ │ cannot function │
│ │ │ │ with file │
│ │ │ │ descriptors above │
│ │ │ │ 1023 on Linux. │
│ │ │ │ Nowadays, the │
│ │ │ │ hard limit │
│ │ │ │ defaults to │
│ │ │ │ 524288, a very │
│ │ │ │ high value │
│ │ │ │ compared to │
│ │ │ │ historical │
│ │ │ │ defaults. │
│ │ │ │ Typically │
│ │ │ │ applications │
│ │ │ │ should increase │
│ │ │ │ their soft limit │
│ │ │ │ to the hard limit │
│ │ │ │ on their own, if │
│ │ │ │ they are OK with │
│ │ │ │ working with file │
│ │ │ │ descriptors above │
│ │ │ │ 1023, i.e. do not │
│ │ │ │ use select(2). │
│ │ │ │ Note that file │
│ │ │ │ descriptors are │
│ │ │ │ nowadays │
│ │ │ │ accounted like │
│ │ │ │ any other form of │
│ │ │ │ memory, thus │
│ │ │ │ there should not │
│ │ │ │ be any need to │
│ │ │ │ lower the hard │
│ │ │ │ limit. Use │
│ │ │ │ MemoryMax= to │
│ │ │ │ control overall │
│ │ │ │ service memory │
│ │ │ │ use, including │
│ │ │ │ file descriptor │
│ │ │ │ memory. │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitAS= │ ulimit -v │ Bytes │ Do not use. This │
│ │ │ │ limits the │
│ │ │ │ allowed address │
│ │ │ │ range, not memory │
│ │ │ │ use! Defaults to │
│ │ │ │ unlimited and │
│ │ │ │ should not be │
│ │ │ │ lowered. To limit │
│ │ │ │ memory use, see │
│ │ │ │ MemoryMax= in │
│ │ │ │ systemd.resource- │
│ │ │ │ control(5). │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitNPROC= │ ulimit -u │ Number of │ This limit is │
│ │ │ Processes │ enforced based on │
│ │ │ │ the number of │
│ │ │ │ processes │
│ │ │ │ belonging to the │
│ │ │ │ user. Typically │
│ │ │ │ it is better to │
│ │ │ │ track processes │
│ │ │ │ per service, i.e. │
│ │ │ │ use TasksMax=, │
│ │ │ │ see │
│ │ │ │ systemd.resource- │
│ │ │ │ control(5). │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitMEMLOCK= │ ulimit -l │ Bytes │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitLOCKS= │ ulimit -x │ Number of Locks │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitSIGPENDING= │ ulimit -i │ Number of Queued │ - │
│ │ │ Signals │ │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitMSGQUEUE= │ ulimit -q │ Bytes │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitNICE= │ ulimit -e │ Nice Level │ - │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitRTPRIO= │ ulimit -r │ Realtime │ - │
│ │ │ Priority │ │
├──────────────────┼────────────┼──────────────────┼───────────────────┤
│ LimitRTTIME= │ ulimit -R │ Microseconds │ - │
└──────────────────┴────────────┴──────────────────┴───────────────────┘

UMask=
Controls the file mode creation mask. Takes an access mode in octal
notation. See umask(2) for details. Defaults to 0022 for system
units. For user units the default value is inherited from the
per-user service manager (whose default is in turn inherited from
the system service manager, and thus typically also is 0022 — unless
overridden by a PAM module). In order to change the per-user mask
for all user services, consider setting the UMask= setting of the
user's user@.service system service instance. The per-user umask may
also be set via the umask field of a user's JSON User Record[5] (for
users managed by systemd-homed.service(8) this field may be
controlled via homectl --umask=). It may also be set via a PAM
module, such as pam_umask(8).

CoredumpFilter=
Controls which types of memory mappings will be saved if the process
dumps core (using the /proc/pid/coredump_filter file). Takes a
whitespace-separated combination of mapping type names or numbers
(with the default base 16). Mapping type names are
private-anonymous, shared-anonymous, private-file-backed,
shared-file-backed, elf-headers, private-huge, shared-huge,
private-dax, shared-dax, and the special values all (all types) and
default (the kernel default of "private-anonymous shared-anonymous
elf-headers private-huge"). See core(5) for the meaning of the
mapping types. When specified multiple times, all specified masks
are ORed. When not set, or if the empty value is assigned, the
inherited value is not changed.

Example 2. Add DAX pages to the dump filter

CoredumpFilter=default private-dax shared-dax

Added in version 246.

KeyringMode=
Controls how the kernel session keyring is set up for the service
(see session-keyring(7) for details on the session keyring). Takes
one of inherit, private, shared. If set to inherit no special
keyring setup is done, and the kernel's default behaviour is
applied. If private is used a new session keyring is allocated when
a service process is invoked, and it is not linked up with any user
keyring. This is the recommended setting for system services, as
this ensures that multiple services running under the same system
user ID (in particular the root user) do not share their key
material among each other. If shared is used a new session keyring
is allocated as for private, but the user keyring of the user
configured with User= is linked into it, so that keys assigned to
the user may be requested by the unit's processes. In this mode
multiple units running processes under the same user ID may share
key material. Unless inherit is selected the unique invocation ID
for the unit (see below) is added as a protected key by the name
"invocation_id" to the newly created session keyring. Defaults to
private for services of the system service manager and to inherit
for non-service units and for services of the user service manager.

Added in version 235.

OOMScoreAdjust=
Sets the adjustment value for the Linux kernel's Out-Of-Memory (OOM)
killer score for executed processes. Takes an integer between -1000
(to disable OOM killing of processes of this unit) and 1000 (to make
killing of processes of this unit under memory pressure very
likely). See The /proc Filesystem[6] for details. If not specified
defaults to the OOM score adjustment level of the service manager
itself, which is normally at 0.

Use the OOMPolicy= setting of service units to configure how the
service manager shall react to the kernel OOM killer or systemd-oomd
terminating a process of the service. See systemd.service(5) for
details.

TimerSlackNSec=
Sets the timer slack in nanoseconds for the executed processes. The
timer slack controls the accuracy of wake-ups triggered by timers.
See prctl(2) for more information. Note that in contrast to most
other time span definitions this parameter takes an integer value in
nano-seconds if no unit is specified. The usual time units are
understood too.

Personality=
Controls which kernel architecture uname(2) shall report, when
invoked by unit processes. Takes one of the architecture identifiers
arm64, arm64-be, arm, arm-be, x86, x86-64, ppc, ppc-le, ppc64,
ppc64-le, s390 or s390x. Which personality architectures are
supported depends on the kernel's native architecture. Usually the
64-bit versions of the various system architectures support their
immediate 32-bit personality architecture counterpart, but no
others. For example, x86-64 systems support the x86-64 and x86
personalities but no others. The personality feature is useful when
running 32-bit services on a 64-bit host system. If not specified,
the personality is left unmodified and thus reflects the personality
of the host system's kernel. This option is not useful on
architectures for which only one native word width was ever
available, such as m68k (32-bit only) or alpha (64-bit only).

Added in version 209.

IgnoreSIGPIPE=
Takes a boolean argument. If true, SIGPIPE is ignored in the
executed process. Defaults to true since SIGPIPE is generally only
useful in shell pipelines.

SCHEDULING
Nice=
Sets the default nice level (scheduling priority) for executed
processes. Takes an integer between -20 (highest priority) and 19
(lowest priority). In case of resource contention, smaller values
mean more resources will be made available to the unit's processes,
larger values mean less resources will be made available. See
setpriority(2) for details.

CPUSchedulingPolicy=
Sets the CPU scheduling policy for executed processes. Takes one of
other, batch, idle, fifo or rr. See sched_setscheduler(2) for
details.

CPUSchedulingPriority=
Sets the CPU scheduling priority for executed processes. The
available priority range depends on the selected CPU scheduling
policy (see above). For real-time scheduling policies an integer
between 1 (lowest priority) and 99 (highest priority) can be used.
In case of CPU resource contention, smaller values mean less CPU
time is made available to the service, larger values mean more. See
sched_setscheduler(2) for details.

CPUSchedulingResetOnFork=
Takes a boolean argument. If true, elevated CPU scheduling
priorities and policies will be reset when the executed processes
call fork(2), and can hence not leak into child processes. See
sched_setscheduler(2) for details. Defaults to false.

CPUAffinity=
Controls the CPU affinity of the executed processes. Takes a list of
CPU indices or ranges separated by either whitespace or commas.
Alternatively, takes a special "numa" value in which case systemd
automatically derives allowed CPU range based on the value of
NUMAMask= option. CPU ranges are specified by the lower and upper
CPU indices separated by a dash. This option may be specified more
than once, in which case the specified CPU affinity masks are
merged. If the empty string is assigned, the mask is reset, all
assignments prior to this will have no effect. See
sched_setaffinity(2) for details.

NUMAPolicy=
Controls the NUMA memory policy of the executed processes. Takes a
policy type, one of: default, preferred, bind, interleave and local.
A list of NUMA nodes that should be associated with the policy must
be specified in NUMAMask=. For more details on each policy please
see, set_mempolicy(2). For overall overview of NUMA support in Linux
see, numa(7).

Added in version 243.

NUMAMask=
Controls the NUMA node list which will be applied alongside with
selected NUMA policy. Takes a list of NUMA nodes and has the same
syntax as a list of CPUs for CPUAffinity= option or special "all"
value which will include all available NUMA nodes in the mask. Note
that the list of NUMA nodes is not required for default and local
policies and for preferred policy we expect a single NUMA node.

Added in version 243.

IOSchedulingClass=
Sets the I/O scheduling class for executed processes. Takes one of
the strings realtime, best-effort or idle. The kernel's default
scheduling class is best-effort at a priority of 4. If the empty
string is assigned to this option, all prior assignments to both
IOSchedulingClass= and IOSchedulingPriority= have no effect. See
ioprio_set(2) for details.

IOSchedulingPriority=
Sets the I/O scheduling priority for executed processes. Takes an
integer between 0 (highest priority) and 7 (lowest priority). In
case of I/O contention, smaller values mean more I/O bandwidth is
made available to the unit's processes, larger values mean less
bandwidth. The available priorities depend on the selected I/O
scheduling class (see above). If the empty string is assigned to
this option, all prior assignments to both IOSchedulingClass= and
IOSchedulingPriority= have no effect. For the kernel's default
scheduling class (best-effort) this defaults to 4. See ioprio_set(2)
for details.

SANDBOXING
The following sandboxing options are an effective way to limit the
exposure of the system towards the unit's processes. It is recommended
to turn on as many of these options for each unit as is possible without
negatively affecting the process' ability to operate. Note that many of
these sandboxing features are gracefully turned off on systems where the
underlying security mechanism is not available. For example,
ProtectSystem= has no effect if the kernel is built without file system
namespacing or if the service manager runs in a container manager that
makes file system namespacing unavailable to its payload. Similarly,
RestrictRealtime= has no effect on systems that lack support for SECCOMP
system call filtering, or in containers where support for this is turned
off.

Also note that some sandboxing functionality is generally not available
in user services (i.e. services run by the per-user service manager).
Specifically, the various settings requiring file system namespacing
support (such as ProtectSystem=) are not available, as the underlying
kernel functionality is only accessible to privileged processes.
However, most namespacing settings, that will not work on their own in
user services, will work when used in conjunction with
PrivateUsers=true.

Note that the various options that turn directories read-only (such as
ProtectSystem=, ReadOnlyPaths=, ...) do not affect the ability for
programs to connect to and communicate with AF_UNIX sockets in these
directories. These options cannot be used to lock down access to IPC
services hence.

ProtectSystem=
Takes a boolean argument or the special values "full" or "strict".
If true, mounts the /usr/ and the boot loader directories (/boot and
/efi) read-only for processes invoked by this unit. If set to
"full", the /etc/ directory is mounted read-only, too. If set to
"strict" the entire file system hierarchy is mounted read-only,
except for the API file system subtrees /dev/, /proc/ and /sys/
(protect these directories using PrivateDevices=,
ProtectKernelTunables=, ProtectControlGroups=). This setting ensures
that any modification of the vendor-supplied operating system (and
optionally its configuration, and local mounts) is prohibited for
the service. It is recommended to enable this setting for all
long-running services, unless they are involved with system updates
or need to modify the operating system in other ways. If this option
is used, ReadWritePaths= may be used to exclude specific directories
from being made read-only. Similar, StateDirectory=, LogsDirectory=,
... and related directory settings (see below) also exclude the
specific directories from the effect of ProtectSystem=. This setting
is implied if DynamicUser= is set. This setting cannot ensure
protection in all cases. In general it has the same limitations as
ReadOnlyPaths=, see below. Defaults to off.

Note that if ProtectSystem= is set to "strict" and PrivateTmp= is
enabled, then /tmp/ and /var/tmp/ will be writable.

Added in version 214.

ProtectHome=
Takes a boolean argument or the special values "read-only" or
"tmpfs". If true, the directories /home/, /root, and /run/user are
made inaccessible and empty for processes invoked by this unit. If
set to "read-only", the three directories are made read-only
instead. If set to "tmpfs", temporary file systems are mounted on
the three directories in read-only mode. The value "tmpfs" is useful
to hide home directories not relevant to the processes invoked by
the unit, while still allowing necessary directories to be made
visible when listed in BindPaths= or BindReadOnlyPaths=.

Setting this to "yes" is mostly equivalent to setting the three
directories in InaccessiblePaths=. Similarly, "read-only" is mostly
equivalent to ReadOnlyPaths=, and "tmpfs" is mostly equivalent to
TemporaryFileSystem= with ":ro".

It is recommended to enable this setting for all long-running
services (in particular network-facing ones), to ensure they cannot
get access to private user data, unless the services actually
require access to the user's private data. This setting is implied
if DynamicUser= is set. This setting cannot ensure protection in all
cases. In general it has the same limitations as ReadOnlyPaths=, see
below.

Added in version 214.

RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=,
ConfigurationDirectory=
These options take a whitespace-separated list of directory names.
The specified directory names must be relative, and may not include
"..". If set, when the unit is started, one or more directories by
the specified names will be created (including their parents) below
the locations defined in the following table. Also, the
corresponding environment variable will be defined with the full
paths of the directories. If multiple directories are set, then in
the environment variable the paths are concatenated with colon
(":").

If DynamicUser= is used, and if the kernel version supports
id-mapped mounts[7], the specified directories will be owned by
"nobody" in the host namespace and will be mapped to (and will be
owned by) the service's UID/GID in its own namespace. For backward
compatibility, existing directories created without id-mapped mounts
will be kept untouched.

Table 2. Automatic directory creation and environment variables
┌─────────────────────────┬────────────────┬──────────────────────┬──────────────────────────┐
│ Directory │ Below path for │ Below path for │ Environment │
│ │ system units │ user units │ variable set │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ RuntimeDirectory= │ /run/ │ $XDG_RUNTIME_DIR │ $RUNTIME_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ StateDirectory= │ /var/lib/ │ $XDG_STATE_HOME │ $STATE_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ CacheDirectory= │ /var/cache/ │ $XDG_CACHE_HOME │ $CACHE_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ LogsDirectory= │ /var/log/ │ $XDG_STATE_HOME/log/ │ $LOGS_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ ConfigurationDirectory= │ /etc/ │ $XDG_CONFIG_HOME │ $CONFIGURATION_DIRECTORY │
└─────────────────────────┴────────────────┴──────────────────────┴──────────────────────────┘

In case of RuntimeDirectory= the innermost subdirectories are
removed when the unit is stopped. It is possible to preserve the
specified directories in this case if RuntimeDirectoryPreserve= is
configured to restart or yes (see below). The directories specified
with StateDirectory=, CacheDirectory=, LogsDirectory=,
ConfigurationDirectory= are not removed when the unit is stopped.

Except in case of ConfigurationDirectory=, the innermost specified
directories will be owned by the user and group specified in User=
and Group=. If the specified directories already exist and their
owning user or group do not match the configured ones, all files and
directories below the specified directories as well as the
directories themselves will have their file ownership recursively
changed to match what is configured. As an optimization, if the
specified directories are already owned by the right user and group,
files and directories below of them are left as-is, even if they do
not match what is requested. The innermost specified directories
will have their access mode adjusted to the what is specified in
RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=,
LogsDirectoryMode= and ConfigurationDirectoryMode=.

These options imply BindPaths= for the specified paths. When
combined with RootDirectory= or RootImage= these paths always reside
on the host and are mounted from there into the unit's file system
namespace.

If DynamicUser= is used, the logic for CacheDirectory=,
LogsDirectory= and StateDirectory= is slightly altered: the
directories are created below /var/cache/private, /var/log/private
and /var/lib/private, respectively, which are host directories made
inaccessible to unprivileged users, which ensures that access to
these directories cannot be gained through dynamic user ID
recycling. Symbolic links are created to hide this difference in
behaviour. Both from perspective of the host and from inside the
unit, the relevant directories hence always appear directly below
/var/cache, /var/log and /var/lib.

Use RuntimeDirectory= to manage one or more runtime directories for
the unit and bind their lifetime to the daemon runtime. This is
particularly useful for unprivileged daemons that cannot create
runtime directories in /run/ due to lack of privileges, and to make
sure the runtime directory is cleaned up automatically after use.
For runtime directories that require more complex or different
configuration or lifetime guarantees, please consider using
tmpfiles.d(5).

RuntimeDirectory=, StateDirectory=, CacheDirectory= and
LogsDirectory= optionally support two more parameters, separated by
":". The second parameter will be interpreted as a destination path
that will be created as a symlink to the directory. The symlinks
will be created after any BindPaths= or TemporaryFileSystem= options
have been set up, to make ephemeral symlinking possible. The same
source can have multiple symlinks, by using the same first
parameter, but a different second parameter. The third parameter is
a flags field, and since v257 can take a value of ro to make the
directory read only for the service. This is also supported for
ConfigurationDirectory=. If multiple symlinks are set up, the
directory will be read only if at least one is configured to be read
only. To pass a flag without a destination symlink, the second
parameter can be empty, for example:

ConfigurationDirectory=foo::ro

The directories defined by these options are always created under
the standard paths used by systemd (/var/, /run/, /etc/, ...). If
the service needs directories in a different location, a different
mechanism has to be used to create them.

tmpfiles.d(5) provides functionality that overlaps with these
options. Using these options is recommended, because the lifetime of
the directories is tied directly to the lifetime of the unit, and it
is not necessary to ensure that the tmpfiles.d configuration is
executed before the unit is started.

To remove any of the directories created by these settings, use the
systemctl clean ... command on the relevant units, see systemctl(1)
for details.

Example: if a system service unit has the following,

RuntimeDirectory=foo/bar baz

the service manager creates /run/foo (if it does not exist),
/run/foo/bar, and /run/baz. The directories /run/foo/bar and
/run/baz except /run/foo are owned by the user and group specified
in User= and Group=, and removed when the service is stopped.

Example: if a system service unit has the following,

RuntimeDirectory=foo/bar
StateDirectory=aaa/bbb ccc

then the environment variable "RUNTIME_DIRECTORY" is set with
"/run/foo/bar", and "STATE_DIRECTORY" is set with
"/var/lib/aaa/bbb:/var/lib/ccc".

Example: if a system service unit has the following,

RuntimeDirectory=foo:bar foo:baz

the service manager creates /run/foo (if it does not exist), and
/run/bar plus /run/baz as symlinks to /run/foo.

Added in version 211.

RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=,
LogsDirectoryMode=, ConfigurationDirectoryMode=
Specifies the access mode of the directories specified in
RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=,
or ConfigurationDirectory=, respectively, as an octal number.
Defaults to 0755. See "Permissions" in path_resolution(7) for a
discussion of the meaning of permission bits.

Added in version 234.

RuntimeDirectoryPreserve=
Takes a boolean argument or restart. If set to no (the default), the
directories specified in RuntimeDirectory= are always removed when
the service stops. If set to restart the directories are preserved
when the service is both automatically and manually restarted. Here,
the automatic restart means the operation specified in Restart=, and
manual restart means the one triggered by systemctl restart
foo.service. If set to yes, then the directories are not removed
when the service is stopped. Note that since the runtime directory
/run/ is a mount point of "tmpfs", then for system services the
directories specified in RuntimeDirectory= are removed when the
system is rebooted.

Added in version 235.

TimeoutCleanSec=
Configures a timeout on the clean-up operation requested through
systemctl clean ..., see systemctl(1) for details. Takes the usual
time values and defaults to infinity, i.e. by default no timeout is
applied. If a timeout is configured the clean operation will be
aborted forcibly when the timeout is reached, potentially leaving
resources on disk.

Added in version 244.

ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths=,
NoExecPaths=
Sets up a new file system namespace for executed processes. These
options may be used to limit access a process has to the file
system. Each setting takes a space-separated list of paths relative
to the host's root directory (i.e. the system running the service
manager). Note that if paths contain symlinks, they are resolved
relative to the root directory set with RootDirectory=/RootImage=.

Paths listed in ReadWritePaths= are accessible from within the
namespace with the same access modes as from outside of it. Paths
listed in ReadOnlyPaths= are accessible for reading only, writing
will be refused even if the usual file access controls would permit
this. Nest ReadWritePaths= inside of ReadOnlyPaths= in order to
provide writable subdirectories within read-only directories. Use
ReadWritePaths= in order to allow-list specific paths for write
access if ProtectSystem=strict is used. Note that ReadWritePaths=
cannot be used to gain write access to a file system whose
superblock is mounted read-only. On Linux, for each mount point
write access is granted only if the mount point itself and the file
system superblock backing it are not marked read-only.
ReadWritePaths= only controls the former, not the latter, hence a
read-only file system superblock remains protected.

Paths listed in InaccessiblePaths= will be made inaccessible for
processes inside the namespace along with everything below them in
the file system hierarchy. This may be more restrictive than
desired, because it is not possible to nest ReadWritePaths=,
ReadOnlyPaths=, BindPaths=, or BindReadOnlyPaths= inside it. For a
more flexible option, see TemporaryFileSystem=.

Content in paths listed in NoExecPaths= are not executable even if
the usual file access controls would permit this. Nest ExecPaths=
inside of NoExecPaths= in order to provide executable content within
non-executable directories.

Non-directory paths may be specified as well. These options may be
specified more than once, in which case all paths listed will have
limited access from within the namespace. If the empty string is
assigned to this option, the specific list is reset, and all prior
assignments have no effect.

Paths in ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=,
ExecPaths= and NoExecPaths= may be prefixed with "-", in which case
they will be ignored when they do not exist. If prefixed with "+"
the paths are taken relative to the root directory of the unit, as
configured with RootDirectory=/RootImage=, instead of relative to
the root directory of the host (see above). When combining "-" and
"+" on the same path make sure to specify "-" first, and "+" second.

Note that these settings will disconnect propagation of mounts from
the unit's processes to the host. This means that this setting may
not be used for services which shall be able to install mount points
in the main mount namespace. For ReadWritePaths= and ReadOnlyPaths=,
propagation in the other direction is not affected, i.e. mounts
created on the host generally appear in the unit processes'
namespace, and mounts removed on the host also disappear there too.
In particular, note that mount propagation from host to unit will
result in unmodified mounts to be created in the unit's namespace,
i.e. writable mounts appearing on the host will be writable in the
unit's namespace too, even when propagated below a path marked with
ReadOnlyPaths=! Restricting access with these options hence does not
extend to submounts of a directory that are created later on. This
means the lock-down offered by that setting is not complete, and
does not offer full protection.

Note that the effect of these settings may be undone by privileged
processes. In order to set up an effective sandboxed environment for
a unit it is thus recommended to combine these settings with either
CapabilityBoundingSet=~CAP_SYS_ADMIN or SystemCallFilter=~@mount.

Please be extra careful when applying these options to API file
systems (a list of them could be found in MountAPIVPS=), since they
may be required for basic system functionalities. Moreover, /run/
needs to be writable for setting up mount namespace and propagation.

Simple allow-list example using these directives:

[Service]
ReadOnlyPaths=/
ReadWritePaths=/var /run
InaccessiblePaths=-/lost+found
NoExecPaths=/
ExecPaths=/usr/sbin/my_daemon /usr/lib /usr/lib64

These options are only available for system services, or for
services running in per-user instances of the service manager in
which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the kernel via
the "kernel.unprivileged_userns_clone=" sysctl).

Added in version 231.

TemporaryFileSystem=
Takes a space-separated list of mount points for temporary file
systems (tmpfs). If set, a new file system namespace is set up for
executed processes, and a temporary file system is mounted on each
mount point. This option may be specified more than once, in which
case temporary file systems are mounted on all listed mount points.
If the empty string is assigned to this option, the list is reset,
and all prior assignments have no effect. Each mount point may
optionally be suffixed with a colon (":") and mount options such as
"size=10%" or "ro". By default, each temporary file system is
mounted with "nodev,strictatime,mode=0755". These can be disabled by
explicitly specifying the corresponding mount options, e.g., "dev"
or "nostrictatime".

This is useful to hide files or directories not relevant to the
processes invoked by the unit, while necessary files or directories
can be still accessed by combining with BindPaths= or
BindReadOnlyPaths=:

Example: if a unit has the following,

TemporaryFileSystem=/var:ro
BindReadOnlyPaths=/var/lib/systemd

then the invoked processes by the unit cannot see any files or
directories under /var/ except for /var/lib/systemd or its contents.

Added in version 238.

PrivateTmp=
Takes a boolean argument, or "disconnected". If enabled, a new file
system namespace will be set up for the executed processes, and
/tmp/ and /var/tmp/ directories inside it are not shared with
processes outside of the namespace, plus all temporary files created
by a service in these directories will be removed after the service
is stopped. If "true", the backing storage of the private temporary
directories will remain on the host's /tmp/ and /var/tmp/
directories. If "disconnected", the directories will be backed by a
completely new tmpfs instance, meaning that the storage is fully
disconnected from the host namespace. Defaults to false.

This setting is useful to secure access to temporary files of the
process, but makes sharing between processes via /tmp/ or /var/tmp/
impossible. If not set to "disconnected", it is possible to run two
or more units within the same private /tmp/ and /var/tmp/ namespace
by using the JoinsNamespaceOf= directive, see systemd.unit(5) for
details. This setting is implied if DynamicUser= is set. For this
setting, the same restrictions regarding mount propagation and
privileges apply as for ReadOnlyPaths= and related calls, see above.
If set to "true" (as opposed to "disconnected"), this has the side
effect of adding Requires= and After= dependencies on all mount
units necessary to access /tmp/ and /var/tmp/ on the host. Moreover
an implicitly After= ordering on systemd-tmpfiles-setup.service(8)
is added.

Note that the implementation of this setting might be impossible
(for example if mount namespaces are not available), and the unit
should be written in a way that does not solely rely on this setting
for security.

PrivateDevices=
Takes a boolean argument. If true, sets up a new /dev/ mount for the
executed processes and only adds API pseudo devices such as
/dev/null, /dev/zero or /dev/random (as well as the pseudo TTY
subsystem) to it, but no physical devices such as /dev/sda, system
memory /dev/mem, system ports /dev/port and others. This is useful
to turn off physical device access by the executed process. Defaults
to false.

Enabling this option will install a system call filter to block
low-level I/O system calls that are grouped in the @raw-io set,
remove CAP_MKNOD and CAP_SYS_RAWIO from the capability bounding set
for the unit, and set DevicePolicy=closed (see systemd.resource-
control(5) for details). Note that using this setting will
disconnect propagation of mounts from the service to the host
(propagation in the opposite direction continues to work). This
means that this setting may not be used for services which shall be
able to install mount points in the main mount namespace. The new
/dev/ will be mounted read-only and 'noexec'. The latter may break
old programs which try to set up executable memory by using mmap(2)
of /dev/zero instead of using MAP_ANON. For this setting the same
restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above.

When access to some but not all devices must be possible, the
DeviceAllow= setting might be used instead. See systemd.resource-
control(5).

Added in version 209.

PrivateNetwork=
Takes a boolean argument. If true, sets up a new network namespace
for the executed processes and configures only the loopback network
device "lo" inside it. No other network devices will be available to
the executed process. This is useful to turn off network access by
the executed process. Defaults to false. It is possible to run two
or more units within the same private network namespace by using the
JoinsNamespaceOf= directive, see systemd.unit(5) for details. Note
that this option will disconnect all socket families from the host,
including AF_NETLINK and AF_UNIX. Effectively, for AF_NETLINK this
means that device configuration events received from systemd-
udevd.service(8) are not delivered to the unit's processes. And for
AF_UNIX this has the effect that AF_UNIX sockets in the abstract
socket namespace of the host will become unavailable to the unit's
processes (however, those located in the file system will continue
to be accessible).

Note that the implementation of this setting might be impossible
(for example if network namespaces are not available), and the unit
should be written in a way that does not solely rely on this setting
for security.

When this option is enabled, PrivateMounts= is implied unless it is
explicitly disabled, and /sys will be remounted to associate it with
the new network namespace.

When this option is used on a socket unit any sockets bound on
behalf of this unit will be bound within a private network
namespace. This may be combined with JoinsNamespaceOf= to listen on
sockets inside of network namespaces of other services.

NetworkNamespacePath=
Takes an absolute file system path referring to a Linux network
namespace pseudo-file (i.e. a file like /proc/$PID/ns/net or a bind
mount or symlink to one). When set the invoked processes are added
to the network namespace referenced by that path. The path has to
point to a valid namespace file at the moment the processes are
forked off. If this option is used PrivateNetwork= has no effect. If
this option is used together with JoinsNamespaceOf= then it only has
an effect if this unit is started before any of the listed units
that have PrivateNetwork= or NetworkNamespacePath= configured, as
otherwise the network namespace of those units is reused.

When this option is enabled, PrivateMounts= is implied unless it is
explicitly disabled, and /sys will be remounted to associate it with
the new network namespace.

When this option is used on a socket unit any sockets bound on
behalf of this unit will be bound within the specified network
namespace.

Added in version 242.

PrivateIPC=
Takes a boolean argument. If true, sets up a new IPC namespace for
the executed processes. Each IPC namespace has its own set of System
V IPC identifiers and its own POSIX message queue file system. This
is useful to avoid name clash of IPC identifiers. Defaults to false.
It is possible to run two or more units within the same private IPC
namespace by using the JoinsNamespaceOf= directive, see
systemd.unit(5) for details.

Note that IPC namespacing does not have an effect on AF_UNIX
sockets, which are the most common form of IPC used on Linux.
Instead, AF_UNIX sockets in the file system are subject to mount
namespacing, and those in the abstract namespace are subject to
network namespacing. IPC namespacing only has an effect on SysV IPC
(which is mostly legacy) as well as POSIX message queues (for which
AF_UNIX/SOCK_SEQPACKET sockets are typically a better replacement).
IPC namespacing also has no effect on POSIX shared memory (which is
subject to mount namespacing) either. See ipc_namespaces(7) for the
details.

Note that the implementation of this setting might be impossible
(for example if IPC namespaces are not available), and the unit
should be written in a way that does not solely rely on this setting
for security.

Added in version 248.

IPCNamespacePath=
Takes an absolute file system path referring to a Linux IPC
namespace pseudo-file (i.e. a file like /proc/$PID/ns/ipc or a bind
mount or symlink to one). When set the invoked processes are added
to the network namespace referenced by that path. The path has to
point to a valid namespace file at the moment the processes are
forked off. If this option is used PrivateIPC= has no effect. If
this option is used together with JoinsNamespaceOf= then it only has
an effect if this unit is started before any of the listed units
that have PrivateIPC= or IPCNamespacePath= configured, as otherwise
the network namespace of those units is reused.

Added in version 248.

MemoryKSM=
Takes a boolean argument. When set, it enables KSM (kernel samepage
merging) for the processes. KSM is a memory-saving de-duplication
feature. Anonymous memory pages with identical content can be
replaced by a single write-protected page. This feature should only
be enabled for jobs that share the same security domain. For
details, see Kernel Samepage Merging[8] in the kernel documentation.

Note that this functionality might not be available, for example if
KSM is disabled in the kernel, or the kernel does not support
controlling KSM at the process level through prctl(2).

Added in version 254.

PrivatePIDs=
Takes a boolean argument. Defaults to false. If enabled, sets up a
new PID namespace for the executed processes. Each executed process
is now PID 1 - the init process - in the new namespace. /proc/ is
mounted such that only processes in the PID namespace are visible.
If PrivatePIDs= is set, MountAPIVFS=yes is implied.

PrivatePIDs= is only supported for service units. This setting is
not supported with Type=forking since the kernel will kill all
processes in the PID namespace if the init process terminates.

This setting will be ignored if the kernel does not support PID
namespaces.

Note unprivileged user services (i.e. a service run by the per-user
instance of the service manager) will fail with PrivatePIDs=yes if
/proc/ is masked (i.e. /proc/kmsg is over-mounted with tmpfs like
systemd-nspawn(1) does). This is due to a kernel restriction not
allowing unprivileged user namespaces to mount a less restrictive
instance of /proc/.

Added in version 257.

PrivateUsers=
Takes a boolean argument or one of "self" or "identity". Defaults to
false. If enabled, sets up a new user namespace for the executed
processes and configures a user and group mapping. If set to a true
value or "self", a minimal user and group mapping is configured that
maps the "root" user and group as well as the unit's own user and
group to themselves and everything else to the "nobody" user and
group. This is useful to securely detach the user and group
databases used by the unit from the rest of the system, and thus to
create an effective sandbox environment. All files, directories,
processes, IPC objects and other resources owned by users/groups not
equaling "root" or the unit's own will stay visible from within the
unit but appear owned by the "nobody" user and group.

If the parameter is "identity", user namespacing is set up with an
identity mapping for the first 65536 UIDs/GIDs. Any UIDs/GIDs above
65536 will be mapped to the "nobody" user and group, respectively.
While this does not provide UID/GID isolation, since all UIDs/GIDs
are chosen identically it does provide process capability isolation,
and hence is often a good choice if proper user namespacing with
distinct UID maps is not appropriate.

If this mode is enabled, all unit processes are run without
privileges in the host user namespace (regardless if the unit's own
user/group is "root" or not). Specifically this means that the
process will have zero process capabilities on the host's user
namespace, but full capabilities within the service's user
namespace. Settings such as CapabilityBoundingSet= will affect only
the latter, and there's no way to acquire additional capabilities in
the host's user namespace.

When this setting is set up by a per-user instance of the service
manager, the mapping of the "root" user and group to itself is
omitted (unless the user manager is root). Additionally, in the
per-user instance manager case, the user namespace will be set up
before most other namespaces. This means that combining
PrivateUsers=true with other namespaces will enable use of features
not normally supported by the per-user instances of the service
manager.

This setting is particularly useful in conjunction with
RootDirectory=/RootImage=, as the need to synchronize the user and
group databases in the root directory and on the host is reduced, as
the only users and groups who need to be matched are "root",
"nobody" and the unit's own user and group.

Note that the implementation of this setting might be impossible
(for example if user namespaces are not available), and the unit
should be written in a way that does not solely rely on this setting
for security.

Added in version 232.

ProtectHostname=
Takes a boolean argument. When set, sets up a new UTS namespace for
the executed processes. In addition, changing hostname or domainname
is prevented. Defaults to off.

Note that the implementation of this setting might be impossible
(for example if UTS namespaces are not available), and the unit
should be written in a way that does not solely rely on this setting
for security.

Note that when this option is enabled for a service hostname changes
no longer propagate from the system into the service, it is hence
not suitable for services that need to take notice of system
hostname changes dynamically.

Added in version 242.

ProtectClock=
Takes a boolean argument. If set, writes to the hardware clock or
system clock will be denied. Defaults to off. Enabling this option
removes CAP_SYS_TIME and CAP_WAKE_ALARM from the capability bounding
set for this unit, installs a system call filter to block calls that
can set the clock, and DeviceAllow=char-rtc r is implied. Note that
the system calls are blocked altogether, the filter does not take
into account that some of the calls can be used to read the clock
state with some parameter combinations. Effectively, /dev/rtc0,
/dev/rtc1, etc. are made read-only to the service. See
systemd.resource-control(5) for the details about DeviceAllow=.

It is recommended to turn this on for most services that do not need
modify the clock or check its state.

Added in version 245.

ProtectKernelTunables=
Takes a boolean argument. If true, kernel variables accessible
through /proc/sys/, /sys/, /proc/sysrq-trigger, /proc/latency_stats,
/proc/acpi, /proc/timer_stats, /proc/fs and /proc/irq will be made
read-only and /proc/kallsyms as well as /proc/kcore will be
inaccessible to all processes of the unit. Usually, tunable kernel
variables should be initialized only at boot-time, for example with
the sysctl.d(5) mechanism. Few services need to write to these at
runtime; it is hence recommended to turn this on for most services.
For this setting the same restrictions regarding mount propagation
and privileges apply as for ReadOnlyPaths= and related calls, see
above. Defaults to off. Note that this option does not prevent
indirect changes to kernel tunables affected by IPC calls to other
processes. However, InaccessiblePaths= may be used to make relevant
IPC file system objects inaccessible. If ProtectKernelTunables= is
set, MountAPIVFS=yes is implied.

Added in version 232.

ProtectKernelModules=
Takes a boolean argument. If true, explicit module loading will be
denied. This allows module load and unload operations to be turned
off on modular kernels. It is recommended to turn this on for most
services that do not need special file systems or extra kernel
modules to work. Defaults to off. Enabling this option removes
CAP_SYS_MODULE from the capability bounding set for the unit, and
installs a system call filter to block module system calls, also
/usr/lib/modules is made inaccessible. For this setting the same
restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Note that limited
automatic module loading due to user configuration or kernel mapping
tables might still happen as side effect of requested user
operations, both privileged and unprivileged. To disable module
auto-load feature please see sysctl.d(5) kernel.modules_disabled
mechanism and /proc/sys/kernel/modules_disabled documentation.

Added in version 232.

ProtectKernelLogs=
Takes a boolean argument. If true, access to the kernel log ring
buffer will be denied. It is recommended to turn this on for most
services that do not need to read from or write to the kernel log
ring buffer. Enabling this option removes CAP_SYSLOG from the
capability bounding set for this unit, and installs a system call
filter to block the syslog(2) system call (not to be confused with
the libc API syslog(3) for userspace logging). The kernel exposes
its log buffer to userspace via /dev/kmsg and /proc/kmsg. If
enabled, these are made inaccessible to all the processes in the
unit.

Added in version 244.

ProtectControlGroups=
Takes a boolean argument or the special values "private" or
"strict". If true, the Linux Control Groups (cgroups(7)) hierarchies
accessible through /sys/fs/cgroup/ will be made read-only to all
processes of the unit. If set to "private", the unit will run in a
cgroup namespace with a private writable mount of /sys/fs/cgroup/.
If set to "strict", the unit will run in a cgroup namespace with a
private read-only mount of /sys/fs/cgroup/. Defaults to off. If
ProtectControlGroups= is set, MountAPIVFS=yes is implied. Note
"private" and "strict" are downgraded to false and true respectively
unless the system is using the unified control group hierarchy and
the kernel supports cgroup namespaces.

Except for container managers no services should require write
access to the control groups hierarchies; it is hence recommended to
set ProtectControlGroups= to true or "strict" for most services. For
this setting the same restrictions regarding mount propagation and
privileges apply as for ReadOnlyPaths= and related settings, see
above.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 232.

RestrictAddressFamilies=
Restricts the set of socket address families accessible to the
processes of this unit. Takes "none", or a space-separated list of
address family names to allow-list, such as AF_UNIX, AF_INET or
AF_INET6. When "none" is specified, then all address families will
be denied. When prefixed with "~" the listed address families will
be applied as deny list, otherwise as allow list.

By default, no restrictions apply, all address families are
accessible to processes. If assigned the empty string, any previous
address family restriction changes are undone. This setting does not
affect commands prefixed with "+".

Use this option to limit exposure of processes to remote access, in
particular via exotic and sensitive network protocols, such as
AF_PACKET. Note that in most cases, the local AF_UNIX address family
should be included in the configured allow list as it is frequently
used for local communication, including for syslog(2) logging.

Note that this restricts access to the socket(2) system call only.
Sockets passed into the process by other means (for example, by
using socket activation with socket units, see systemd.socket(5))
are unaffected. Also, sockets created with socketpair() (which
creates connected AF_UNIX sockets) or the io_uring(7) functions, are
not affected. Thus, it is recommended to combined this setting with
SystemCallFilter=@service, to only allow a limited subset of system
calls.

Note that this option is limited to some ABIs, in particular x86-64,
but currently has no effect on 32-bit x86, s390, s390x, mips,
mips-le, ppc, ppc-le, ppc64, or ppc64-le, and is ignored. On systems
supporting multiple ABIs (such as x86/x86-64) it is recommended to
turn off alternative ABIs for services, so that they cannot be used
to circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with
SystemCallArchitectures=native or similar.

Added in version 211.

RestrictFileSystems=
Restricts the set of filesystems processes of this unit can open
files on. Takes a space-separated list of filesystem names. Any
filesystem listed is made accessible to the unit's processes, access
to filesystem types not listed is prohibited (allow-listing). If the
first character of the list is "~", the effect is inverted: access
to the filesystems listed is prohibited (deny-listing). If the empty
string is assigned, access to filesystems is not restricted.

If you specify both types of this option (i.e. allow-listing and
deny-listing), the first encountered will take precedence and will
dictate the default action (allow access to the filesystem or deny
it). Then the next occurrences of this option will add or delete the
listed filesystems from the set of the restricted filesystems,
depending on its type and the default action.

Example: if a unit has the following,

RestrictFileSystems=ext4 tmpfs
RestrictFileSystems=ext2 ext4

then access to ext4, tmpfs, and ext2 is allowed and access to other
filesystems is denied.

Example: if a unit has the following,

RestrictFileSystems=ext4 tmpfs
RestrictFileSystems=~ext4

then only access tmpfs is allowed.

Example: if a unit has the following,

RestrictFileSystems=~ext4 tmpfs
RestrictFileSystems=ext4

then only access to tmpfs is denied.

As the number of possible filesystems is large, predefined sets of
filesystems are provided. A set starts with "@" character, followed
by name of the set.

Table 3. Currently predefined filesystem sets
┌───────────────────┬────────────────────────────┐
│ Set │ Description │
├───────────────────┼────────────────────────────┤
│ @basic-api │ Basic filesystem API. │
├───────────────────┼────────────────────────────┤
│ @auxiliary-api │ Auxiliary filesystem API. │
├───────────────────┼────────────────────────────┤
│ @common-block │ Common block device │
│ │ filesystems. │
├───────────────────┼────────────────────────────┤
│ @historical-block │ Historical block device │
│ │ filesystems. │
├───────────────────┼────────────────────────────┤
│ @network │ Well-known network │
│ │ filesystems. │
├───────────────────┼────────────────────────────┤
│ @privileged-api │ Privileged filesystem API. │
├───────────────────┼────────────────────────────┤
│ @temporary │ Temporary filesystems: │
│ │ tmpfs, ramfs. │
├───────────────────┼────────────────────────────┤
│ @known │ All known filesystems │
│ │ defined by the kernel. │
│ │ This list is defined │
│ │ statically in systemd │
│ │ based on a kernel version │
│ │ that was available when │
│ │ this systemd version was │
│ │ released. It will become │
│ │ progressively more │
│ │ out-of-date as the kernel │
│ │ is updated. │
└───────────────────┴────────────────────────────┘

Use systemd-analyze(1)'s filesystems command to retrieve a list of
filesystems defined on the local system.

Note that this setting might not be supported on some systems (for
example if the LSM eBPF hook is not enabled in the underlying kernel
or if not using the unified control group hierarchy). In that case
this setting has no effect.

This option cannot be bypassed by prefixing "+" to the executable
path in the service unit, as it applies to the whole control group.

Added in version 250.

RestrictNamespaces=
Restricts access to Linux namespace functionality for the processes
of this unit. For details about Linux namespaces, see namespaces(7).
Either takes a boolean argument, or a space-separated list of
namespace type identifiers. If false (the default), no restrictions
on namespace creation and switching are made. If true, access to any
kind of namespacing is prohibited. Otherwise, a space-separated list
of namespace type identifiers must be specified, consisting of any
combination of: cgroup, ipc, net, mnt, pid, user and uts. Any
namespace type listed is made accessible to the unit's processes,
access to namespace types not listed is prohibited (allow-listing).
By prepending the list with a single tilde character ("~") the
effect may be inverted: only the listed namespace types will be made
inaccessible, all unlisted ones are permitted (deny-listing). If the
empty string is assigned, the default namespace restrictions are
applied, which is equivalent to false. This option may appear more
than once, in which case the namespace types are merged by OR, or by
AND if the lines are prefixed with "~" (see examples below).
Internally, this setting limits access to the unshare(2), clone(2)
and setns(2) system calls, taking the specified flags parameters
into account. Note that — if this option is used — in addition to
restricting creation and switching of the specified types of
namespaces (or all of them, if true) access to the setns() system
call with a zero flags parameter is prohibited. This setting is only
supported on x86, x86-64, mips, mips-le, mips64, mips64-le,
mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and
enforces no restrictions on other architectures.

Example: if a unit has the following,

RestrictNamespaces=cgroup ipc
RestrictNamespaces=cgroup net

then cgroup, ipc, and net are set. If the second line is prefixed
with "~", e.g.,

RestrictNamespaces=cgroup ipc
RestrictNamespaces=~cgroup net

then, only ipc is set.

Added in version 233.

LockPersonality=
Takes a boolean argument. If set, locks down the personality(2)
system call so that the kernel execution domain may not be changed
from the default or the personality selected with Personality=
directive. This may be useful to improve security, because odd
personality emulations may be poorly tested and source of
vulnerabilities.

Added in version 235.

MemoryDenyWriteExecute=
Takes a boolean argument. If set, attempts to create memory mappings
that are writable and executable at the same time, or to change
existing memory mappings to become executable, or mapping shared
memory segments as executable, are prohibited. Specifically, a
system call filter is added (or preferably, an equivalent kernel
check is enabled with prctl(2)) that rejects mmap(2) system calls
with both PROT_EXEC and PROT_WRITE set, mprotect(2) or
pkey_mprotect(2) system calls with PROT_EXEC set and shmat(2) system
calls with SHM_EXEC set. Note that this option is incompatible with
programs and libraries that generate program code dynamically at
runtime, including JIT execution engines, executable stacks, and
code "trampoline" feature of various C compilers. This option
improves service security, as it makes harder for software exploits
to change running code dynamically. However, the protection can be
circumvented, if the service can write to a filesystem, which is not
mounted with noexec (such as /dev/shm), or it can use
memfd_create(). This can be prevented by making such file systems
inaccessible to the service (e.g. InaccessiblePaths=/dev/shm) and
installing further system call filters
(SystemCallFilter=~memfd_create). Note that this feature is fully
available on x86-64, and partially on x86. Specifically, the shmat()
protection is not available on x86. Note that on systems supporting
multiple ABIs (such as x86/x86-64) it is recommended to turn off
alternative ABIs for services, so that they cannot be used to
circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with
SystemCallArchitectures=native or similar.

Added in version 231.

RestrictRealtime=
Takes a boolean argument. If set, any attempts to enable realtime
scheduling in a process of the unit are refused. This restricts
access to realtime task scheduling policies such as SCHED_FIFO,
SCHED_RR or SCHED_DEADLINE. See sched(7) for details about these
scheduling policies. Realtime scheduling policies may be used to
monopolize CPU time for longer periods of time, and may hence be
used to lock up or otherwise trigger Denial-of-Service situations on
the system. It is hence recommended to restrict access to realtime
scheduling to the few programs that actually require them. Defaults
to off.

Added in version 231.

RestrictSUIDSGID=
Takes a boolean argument. If set, any attempts to set the
set-user-ID (SUID) or set-group-ID (SGID) bits on files or
directories will be denied (for details on these bits see inode(7)).
As the SUID/SGID bits are mechanisms to elevate privileges, and
allow users to acquire the identity of other users, it is
recommended to restrict creation of SUID/SGID files to the few
programs that actually require them. Note that this restricts
marking of any type of file system object with these bits, including
both regular files and directories (where the SGID is a different
meaning than for files, see documentation). This option is implied
if DynamicUser= is enabled. Defaults to off.

Added in version 242.

RemoveIPC=
Takes a boolean parameter. If set, all System V and POSIX IPC
objects owned by the user and group the processes of this unit are
run as are removed when the unit is stopped. This setting only has
an effect if at least one of User=, Group= and DynamicUser= are
used. It has no effect on IPC objects owned by the root user.
Specifically, this removes System V semaphores, as well as System V
and POSIX shared memory segments and message queues. If multiple
units use the same user or group the IPC objects are removed when
the last of these units is stopped. This setting is implied if
DynamicUser= is set.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 232.

PrivateMounts=
Takes a boolean parameter. If set, the processes of this unit will
be run in their own private file system (mount) namespace with all
mount propagation from the processes towards the host's main file
system namespace turned off. This means any file system mount points
established or removed by the unit's processes will be private to
them and not be visible to the host. However, file system mount
points established or removed on the host will be propagated to the
unit's processes. See mount_namespaces(7) for details on file system
namespaces. Defaults to off.

When turned on, this executes three operations for each invoked
process: a new CLONE_NEWNS namespace is created, after which all
existing mounts are remounted to MS_SLAVE to disable propagation
from the unit's processes to the host (but leaving propagation in
the opposite direction in effect). Finally, the mounts are remounted
again to the propagation mode configured with MountFlags=, see
below.

File system namespaces are set up individually for each process
forked off by the service manager. Mounts established in the
namespace of the process created by ExecStartPre= will hence be
cleaned up automatically as soon as that process exits and will not
be available to subsequent processes forked off for ExecStart= (and
similar applies to the various other commands configured for units).
Similarly, JoinsNamespaceOf= does not permit sharing kernel mount
namespaces between units, it only enables sharing of the /tmp/ and
/var/tmp/ directories.

Other file system namespace unit settings — PrivateTmp=,
PrivateDevices=, ProtectSystem=, ProtectHome=, ReadOnlyPaths=,
InaccessiblePaths=, ReadWritePaths=, BindPaths=, BindReadOnlyPaths=,
... — also enable file system namespacing in a fashion equivalent to
this option. Hence it is primarily useful to explicitly request this
behaviour if none of the other settings are used.

Added in version 239.

MountFlags=
Takes a mount propagation setting: shared, slave or private, which
controls whether file system mount points in the file system
namespaces set up for this unit's processes will receive or
propagate mounts and unmounts from other file system namespaces. See
mount(2) for details on mount propagation, and the three propagation
flags in particular.

This setting only controls the final propagation setting in effect
on all mount points of the file system namespace created for each
process of this unit. Other file system namespacing unit settings
(see the discussion in PrivateMounts= above) will implicitly disable
mount and unmount propagation from the unit's processes towards the
host by changing the propagation setting of all mount points in the
unit's file system namespace to slave first. Setting this option to
shared does not reestablish propagation in that case.

If not set – but file system namespaces are enabled through another
file system namespace unit setting – shared mount propagation is
used, but — as mentioned — as slave is applied first, propagation
from the unit's processes to the host is still turned off.

It is not recommended to use private mount propagation for units, as
this means temporary mounts (such as removable media) of the host
will stay mounted and thus indefinitely busy in forked off
processes, as unmount propagation events will not be received by the
file system namespace of the unit.

Usually, it is best to leave this setting unmodified, and use higher
level file system namespacing options instead, in particular
PrivateMounts=, see above.

SYSTEM CALL FILTERING
SystemCallFilter=
Takes a space-separated list of system call names or system call
groups. If this setting is used, system calls executed by the unit
processes except for the listed ones will result in the system call
being denied (allow-listing). If the first character of the list is
"~", the effect is inverted: only the listed system calls will be
denied (deny-listing). This option may be specified more than once,
in which case the filter masks are merged. If the empty string is
assigned, the filter is reset, all prior assignments will have no
effect.

Commands prefixed with "+" are not subject to filtering. The
execve(), exit(), exit_group(), getrlimit(), rt_sigreturn(),
sigreturn() system calls and the system calls for querying time and
sleeping are implicitly allow-listed and do not need to be listed
explicitly.

The default action when a system call is denied is to terminate the
processes with a SIGSYS signal. This can changed using
SystemCallErrorNumber=, see below. In addition, deny-listed system
calls and system call groups may optionally be suffixed with a colon
(":") and an argument in the same format as SystemCallErrorNumber=,
to take this action when the matching system call is made. This
takes precedence over the action specified in
SystemCallErrorNumber=.

This feature makes use of the Secure Computing Mode 2 interfaces of
the kernel ('seccomp filtering') and is useful for enforcing a
minimal sandboxing environment.

Note that on systems supporting multiple ABIs (such as x86/x86-64)
it is recommended to turn off alternative ABIs for services, so that
they cannot be used to circumvent the restrictions of this option.
Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar.

Note that strict system call filters may impact execution and error
handling code paths of the service invocation. Specifically, access
to the execve() system call is required for the execution of the
service binary — if it is blocked service invocation will
necessarily fail. Also, if execution of the service binary fails for
some reason (for example: missing service executable), the error
handling logic might require access to an additional set of system
calls in order to process and log this failure correctly. It might
be necessary to temporarily disable system call filters in order to
allow debugging of such failures.

If you specify both types of this option (i.e. allow-listing and
deny-listing), the first encountered will take precedence and will
dictate the default action (termination or approval of a system
call). Then the next occurrences of this option will add or delete
the listed system calls from the set of the filtered system calls,
depending of its type and the default action. (For example, if you
have started with an allow list rule for read() and write(), and
right after it add a deny list rule for write(), then write() will
be removed from the set.)

As the number of possible system calls is large, predefined groups
of system calls are provided. A group starts with "@" character,
followed by name of the set.

Table 4. Currently predefined system call sets
┌─────────────────┬────────────────────────────┐
│ Set │ Description │
├─────────────────┼────────────────────────────┤
│ @aio │ Asynchronous I/O │
│ │ (io_setup(2), │
│ │ io_submit(2), and related │
│ │ calls) │
├─────────────────┼────────────────────────────┤
│ @basic-io │ System calls for basic │
│ │ I/O: reading, writing, │
│ │ seeking, file descriptor │
│ │ duplication and closing │
│ │ (read(2), write(2), and │
│ │ related calls) │
├─────────────────┼────────────────────────────┤
│ @chown │ Changing file ownership │
│ │ (chown(2), fchownat(2), │
│ │ and related calls) │
├─────────────────┼────────────────────────────┤
│ @clock │ System calls for changing │
│ │ the system clock │
│ │ (adjtimex(2), │
│ │ settimeofday(2), and │
│ │ related calls) │
├─────────────────┼────────────────────────────┤
│ @cpu-emulation │ System calls for CPU │
│ │ emulation functionality │
│ │ (vm86(2) and related │
│ │ calls) │
├─────────────────┼────────────────────────────┤
│ @debug │ Debugging, performance │
│ │ monitoring and tracing │
│ │ functionality (ptrace(2), │
│ │ perf_event_open(2) and │
│ │ related calls) │
├─────────────────┼────────────────────────────┤
│ @file-system │ File system operations: │
│ │ opening, creating files │
│ │ and directories for read │
│ │ and write, renaming and │
│ │ removing them, reading │
│ │ file properties, or │
│ │ creating hard and symbolic │
│ │ links │
├─────────────────┼────────────────────────────┤
│ @io-event │ Event loop system calls │
│ │ (poll(2), select(2), │
│ │ epoll(7), eventfd(2) and │
│ │ related calls) │
├─────────────────┼────────────────────────────┤
│ @ipc │ Pipes, SysV IPC, POSIX │
│ │ Message Queues and other │
│ │ IPC (mq_overview(7), │
│ │ svipc(7)) │
├─────────────────┼────────────────────────────┤
│ @keyring │ Kernel keyring access │
│ │ (keyctl(2) and related │
│ │ calls) │
├─────────────────┼────────────────────────────┤
│ @memlock │ Locking of memory in RAM │
│ │ (mlock(2), mlockall(2) and │
│ │ related calls) │
├─────────────────┼────────────────────────────┤
│ @module │ Loading and unloading of │
│ │ kernel modules │
│ │ (init_module(2), │
│ │ delete_module(2) and │
│ │ related calls) │
├─────────────────┼────────────────────────────┤
│ @mount │ Mounting and unmounting of │
│ │ file systems (mount(2), │
│ │ chroot(2), and related │
│ │ calls) │
├─────────────────┼────────────────────────────┤
│ @network-io │ Socket I/O (including │
│ │ local AF_UNIX): socket(7), │
│ │ unix(7) │
├─────────────────┼────────────────────────────┤
│ @obsolete │ Unusual, obsolete or │
│ │ unimplemented │
│ │ (create_module(2), │
│ │ gtty(2), ...) │
├─────────────────┼────────────────────────────┤
│ @pkey │ System calls that deal │
│ │ with memory protection │
│ │ keys (pkeys(7)) │
├─────────────────┼────────────────────────────┤
│ @privileged │ All system calls which │
│ │ need super-user │
│ │ capabilities │
│ │ (capabilities(7)) │
├─────────────────┼────────────────────────────┤
│ @process │ Process control, │
│ │ execution, namespacing │
│ │ operations (clone(2), │
│ │ kill(2), namespaces(7), │
│ │ ...) │
├─────────────────┼────────────────────────────┤
│ @raw-io │ Raw I/O port access │
│ │ (ioperm(2), iopl(2), │
│ │ pciconfig_read(), ...) │
├─────────────────┼────────────────────────────┤
│ @reboot │ System calls for rebooting │
│ │ and reboot preparation │
│ │ (reboot(2), kexec(), ...) │
├─────────────────┼────────────────────────────┤
│ @resources │ System calls for changing │
│ │ resource limits, memory │
│ │ and scheduling parameters │
│ │ (setrlimit(2), │
│ │ setpriority(2), ...) │
├─────────────────┼────────────────────────────┤
│ @sandbox │ System calls for │
│ │ sandboxing programs │
│ │ (seccomp(2), Landlock │
│ │ system calls, ...) │
├─────────────────┼────────────────────────────┤
│ @setuid │ System calls for changing │
│ │ user ID and group ID │
│ │ credentials, (setuid(2), │
│ │ setgid(2), setresuid(2), │
│ │ ...) │
├─────────────────┼────────────────────────────┤
│ @signal │ System calls for │
│ │ manipulating and handling │
│ │ process signals │
│ │ (signal(2), │
│ │ sigprocmask(2), ...) │
├─────────────────┼────────────────────────────┤
│ @swap │ System calls for │
│ │ enabling/disabling swap │
│ │ devices (swapon(2), │
│ │ swapoff(2)) │
├─────────────────┼────────────────────────────┤
│ @sync │ Synchronizing files and │
│ │ memory to disk (fsync(2), │
│ │ msync(2), and related │
│ │ calls) │
├─────────────────┼────────────────────────────┤
│ @system-service │ A reasonable set of system │
│ │ calls used by common │
│ │ system services, excluding │
│ │ any special purpose calls. │
│ │ This is the recommended │
│ │ starting point for │
│ │ allow-listing system calls │
│ │ for system services, as it │
│ │ contains what is typically │
│ │ needed by system services, │
│ │ but excludes overly │
│ │ specific interfaces. For │
│ │ example, the following │
│ │ APIs are excluded: │
│ │ "@clock", "@mount", │
│ │ "@swap", "@reboot". │
├─────────────────┼────────────────────────────┤
│ @timer │ System calls for │
│ │ scheduling operations by │
│ │ time (alarm(2), │
│ │ timer_create(2), ...) │
├─────────────────┼────────────────────────────┤
│ @known │ All system calls defined │
│ │ by the kernel. This list │
│ │ is defined statically in │
│ │ systemd based on a kernel │
│ │ version that was available │
│ │ when this systemd version │
│ │ was released. It will │
│ │ become progressively more │
│ │ out-of-date as the kernel │
│ │ is updated. │
└─────────────────┴────────────────────────────┘

Note, that as new system calls are added to the kernel, additional
system calls might be added to the groups above. Contents of the
sets may also change between systemd versions. In addition, the list
of system calls depends on the kernel version and architecture for
which systemd was compiled. Use systemd-analyze syscall-filter to
list the actual list of system calls in each filter.

Generally, allow-listing system calls (rather than deny-listing) is
the safer mode of operation. It is recommended to enforce system
call allow lists for all long-running system services. Specifically,
the following lines are a relatively safe basic choice for the
majority of system services:

[Service]
SystemCallFilter=@system-service
SystemCallErrorNumber=EPERM

Note that various kernel system calls are defined redundantly: there
are multiple system calls for executing the same operation. For
example, the pidfd_send_signal() system call may be used to execute
operations similar to what can be done with the older kill() system
call, hence blocking the latter without the former only provides
weak protection. Since new system calls are added regularly to the
kernel as development progresses, keeping system call deny lists
comprehensive requires constant work. It is thus recommended to use
allow-listing instead, which offers the benefit that new system
calls are by default implicitly blocked until the allow list is
updated.

Also note that a number of system calls are required to be
accessible for the dynamic linker to work. The dynamic linker is
required for running most regular programs (specifically: all
dynamic ELF binaries, which is how most distributions build packaged
programs). This means that blocking these system calls (which
include open(), openat() or mmap()) will make most programs
typically shipped with generic distributions unusable.

It is recommended to combine the file system namespacing related
options with SystemCallFilter=~@mount, in order to prohibit the
unit's processes to undo the mappings. Specifically these are the
options PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=,
ProtectKernelTunables=, ProtectControlGroups=, ProtectKernelLogs=,
ProtectClock=, ReadOnlyPaths=, InaccessiblePaths= and
ReadWritePaths=.

Added in version 187.

SystemCallErrorNumber=
Takes an "errno" error number (between 1 and 4095) or errno name
such as EPERM, EACCES or EUCLEAN, to return when the system call
filter configured with SystemCallFilter= is triggered, instead of
terminating the process immediately. See errno(3) for a full list of
error codes. When this setting is not used, or when the empty string
or the special setting "kill" is assigned, the process will be
terminated immediately when the filter is triggered.

Added in version 209.

SystemCallArchitectures=
Takes a space-separated list of architecture identifiers to include
in the system call filter. The known architecture identifiers are
the same as for ConditionArchitecture= described in systemd.unit(5),
as well as x32, mips64-n32, mips64-le-n32, and the special
identifier native. The special identifier native implicitly maps to
the native architecture of the system (or more precisely: to the
architecture the system manager is compiled for). By default, this
option is set to the empty list, i.e. no filtering is applied.

If this setting is used, processes of this unit will only be
permitted to call native system calls, and system calls of the
specified architectures. For the purposes of this option, the x32
architecture is treated as including x86-64 system calls. However,
this setting still fulfills its purpose, as explained below, on x32.

System call filtering is not equally effective on all architectures.
For example, on x86 filtering of network socket-related calls is not
possible, due to ABI limitations — a limitation that x86-64 does not
have, however. On systems supporting multiple ABIs at the same time
— such as x86/x86-64 — it is hence recommended to limit the set of
permitted system call architectures so that secondary ABIs may not
be used to circumvent the restrictions applied to the native ABI of
the system. In particular, setting SystemCallArchitectures=native is
a good choice for disabling non-native ABIs.

System call architectures may also be restricted system-wide via the
SystemCallArchitectures= option in the global configuration. See
systemd-system.conf(5) for details.

Added in version 209.

SystemCallLog=
Takes a space-separated list of system call names. If this setting
is used, all system calls executed by the unit processes for the
listed ones will be logged. If the first character of the list is
"~", the effect is inverted: all system calls except the listed
system calls will be logged. This feature makes use of the Secure
Computing Mode 2 interfaces of the kernel ('seccomp filtering') and
is useful for auditing or setting up a minimal sandboxing
environment. This option may be specified more than once, in which
case the filter masks are merged. If the empty string is assigned,
the filter is reset, all prior assignments will have no effect. This
does not affect commands prefixed with "+".

Added in version 247.

ENVIRONMENT
Environment=
Sets environment variables for executed processes. Each line is
unquoted using the rules described in "Quoting" section in
systemd.syntax(7) and becomes a list of variable assignments. If you
need to assign a value containing spaces or the equals sign to a
variable, put quotes around the whole assignment. Variable expansion
is not performed inside the strings and the "$" character has no
special meaning. Specifier expansion is performed, see the
"Specifiers" section in systemd.unit(5).

This option may be specified more than once, in which case all
listed variables will be set. If the same variable is listed twice,
the later setting will override the earlier setting. If the empty
string is assigned to this option, the list of environment variables
is reset, all prior assignments have no effect.

The names of the variables can contain ASCII letters, digits, and
the underscore character. Variable names cannot be empty or start
with a digit. In variable values, most characters are allowed, but
non-printable characters are currently rejected.

Example:

Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

gives three variables "VAR1", "VAR2", "VAR3" with the values "word1
word2", "word3", "$word 5 6".

See environ(7) for details about environment variables.

Note that environment variables are not suitable for passing secrets
(such as passwords, key material, ...) to service processes.
Environment variables set for a unit are exposed to unprivileged
clients via D-Bus IPC, and generally not understood as being data
that requires protection. Moreover, environment variables are
propagated down the process tree, including across security
boundaries (such as setuid/setgid executables), and hence might leak
to processes that should not have access to the secret data. Use
LoadCredential=, LoadCredentialEncrypted= or SetCredentialEncrypted=
(see below) to pass data to unit processes securely.

EnvironmentFile=
Similar to Environment=, but reads the environment variables from a
text file. The text file should contain newline-separated variable
assignments. Empty lines, lines without an "=" separator, or lines
starting with ";" or "#" will be ignored, which may be used for
commenting. The file must be encoded with UTF-8. Valid characters
are unicode scalar values[9] other than unicode noncharacters[10],
U+0000 NUL, and U+FEFF unicode byte order mark[11]. Control codes
other than NUL are allowed.

In the file, an unquoted value after the "=" is parsed with the same
backslash-escape rules as POSIX shell unquoted text[12], but unlike
in a shell, interior whitespace is preserved and quotes after the
first non-whitespace character are preserved. Leading and trailing
whitespace (space, tab, carriage return) is discarded, but interior
whitespace within the line is preserved verbatim. A line ending with
a backslash will be continued to the following one, with the newline
itself discarded. A backslash "\" followed by any character other
than newline will preserve the following character, so that "\\"
will become the value "\".

In the file, a "'"-quoted value after the "=" can span multiple
lines and contain any character verbatim other than single quote,
like POSIX shell single-quoted text[13]. No backslash-escape
sequences are recognized. Leading and trailing whitespace outside of
the single quotes is discarded.

In the file, a """-quoted value after the "=" can span multiple
lines, and the same escape sequences are recognized as in POSIX
shell double-quoted text[14]. Backslash ("\") followed by any of
""\`$" will preserve that character. A backslash followed by newline
is a line continuation, and the newline itself is discarded. A
backslash followed by any other character is ignored; both the
backslash and the following character are preserved verbatim.
Leading and trailing whitespace outside of the double quotes is
discarded.

The argument passed should be an absolute filename or wildcard
expression, optionally prefixed with "-", which indicates that if
the file does not exist, it will not be read and no error or warning
message is logged. This option may be specified more than once in
which case all specified files are read. If the empty string is
assigned to this option, the list of file to read is reset, all
prior assignments have no effect.

The files listed with this directive will be read shortly before the
process is executed (more specifically, after all processes from a
previous unit state terminated. This means you can generate these
files in one unit state, and read it with this option in the next.
The files are read from the file system of the service manager,
before any file system changes like bind mounts take place).

Settings from these files override settings made with Environment=.
If the same variable is set twice from these files, the files will
be read in the order they are specified and the later setting will
override the earlier setting.

PassEnvironment=
Pass environment variables set for the system service manager to
executed processes. Takes a space-separated list of variable names.
This option may be specified more than once, in which case all
listed variables will be passed. If the empty string is assigned to
this option, the list of environment variables to pass is reset, all
prior assignments have no effect. Variables specified that are not
set for the system manager will not be passed and will be silently
ignored. Note that this option is only relevant for the system
service manager, as system services by default do not automatically
inherit any environment variables set for the service manager
itself. However, in case of the user service manager all environment
variables are passed to the executed processes anyway, hence this
option is without effect for the user service manager.

Variables set for invoked processes due to this setting are subject
to being overridden by those configured with Environment= or
EnvironmentFile=.

Example:

PassEnvironment=VAR1 VAR2 VAR3

passes three variables "VAR1", "VAR2", "VAR3" with the values set
for those variables in PID1.

See environ(7) for details about environment variables.

Added in version 228.

UnsetEnvironment=
Explicitly unset environment variable assignments that would
normally be passed from the service manager to invoked processes of
this unit. Takes a space-separated list of variable names or
variable assignments. This option may be specified more than once,
in which case all listed variables/assignments will be unset. If the
empty string is assigned to this option, the list of environment
variables/assignments to unset is reset. If a variable assignment is
specified (that is: a variable name, followed by "=", followed by
its value), then any environment variable matching this precise
assignment is removed. If a variable name is specified (that is a
variable name without any following "=" or value), then any
assignment matching the variable name, regardless of its value is
removed. Note that the effect of UnsetEnvironment= is applied as
final step when the environment list passed to executed processes is
compiled. That means it may undo assignments from any configuration
source, including assignments made through Environment= or
EnvironmentFile=, inherited from the system manager's global set of
environment variables, inherited via PassEnvironment=, set by the
service manager itself (such as $NOTIFY_SOCKET and such), or set by
a PAM module (in case PAMName= is used).

See "Environment Variables in Spawned Processes" below for a
description of how those settings combine to form the inherited
environment. See environ(7) for general information about
environment variables.

Added in version 235.

LOGGING AND STANDARD INPUT/OUTPUT
StandardInput=
Controls where file descriptor 0 (STDIN) of the executed processes
is connected to. Takes one of null, tty, tty-force, tty-fail, data,
file:path, socket or fd:name.

If null is selected, standard input will be connected to /dev/null,
i.e. all read attempts by the process will result in immediate EOF.

If tty is selected, standard input is connected to a TTY (as
configured by TTYPath=, see below) and the executed process becomes
the controlling process of the terminal. If the terminal is already
being controlled by another process, the executed process waits
until the current controlling process releases the terminal.

tty-force is similar to tty, but the executed process is forcefully
and immediately made the controlling process of the terminal,
potentially removing previous controlling processes from the
terminal.

tty-fail is similar to tty, but if the terminal already has a
controlling process start-up of the executed process fails.

The data option may be used to configure arbitrary textual or binary
data to pass via standard input to the executed process. The data to
pass is configured via StandardInputText=/StandardInputData= (see
below). Note that the actual file descriptor type passed (memory
file, regular file, UNIX pipe, ...) might depend on the kernel and
available privileges. In any case, the file descriptor is read-only,
and when read returns the specified data followed by EOF.

The file:path option may be used to connect a specific file system
object to standard input. An absolute path following the ":"
character is expected, which may refer to a regular file, a FIFO or
special file. If an AF_UNIX socket in the file system is specified,
a stream socket is connected to it. The latter is useful for
connecting standard input of processes to arbitrary system services.

The socket option is valid in socket-activated services only, and
requires the relevant socket unit file (see systemd.socket(5) for
details) to have Accept=yes set, or to specify a single socket only.
If this option is set, standard input will be connected to the
socket the service was activated from, which is primarily useful for
compatibility with daemons designed for use with the traditional
inetd(8) socket activation daemon ($LISTEN_FDS (and related)
environment variables are not passed when socket value is
configured).

The fd:name option connects standard input to a specific, named file
descriptor provided by a socket unit. The name may be specified as
part of this option, following a ":" character (e.g. "fd:foobar").
If no name is specified, the name "stdin" is implied (i.e. "fd" is
equivalent to "fd:stdin"). At least one socket unit defining the
specified name must be provided via the Sockets= option, and the
file descriptor name may differ from the name of its containing
socket unit. If multiple matches are found, the first one will be
used. See FileDescriptorName= in systemd.socket(5) for more details
about named file descriptors and their ordering.

This setting defaults to null, unless
StandardInputText=/StandardInputData= are set, in which case it
defaults to data.

StandardOutput=
Controls where file descriptor 1 (stdout) of the executed processes
is connected to. Takes one of inherit, null, tty, journal, kmsg,
journal+console, kmsg+console, file:path, append:path,
truncate:path, socket or fd:name.

inherit duplicates the file descriptor of standard input for
standard output.

null connects standard output to /dev/null, i.e. everything written
to it will be lost.

tty connects standard output to a tty (as configured via TTYPath=,
see below). If the TTY is used for output only, the executed process
will not become the controlling process of the terminal, and will
not fail or wait for other processes to release the terminal. Note:
if a unit tries to print multiple lines to a TTY during bootup or
shutdown, then there's a chance that those lines will be broken up
by status messages. SetShowStatus() can be used to prevent this
problem. See org.freedesktop.systemd1(5) for details.

journal connects standard output with the journal, which is
accessible via journalctl(1). Note that everything that is written
to kmsg (see below) is implicitly stored in the journal as well, the
specific option listed below is hence a superset of this one. (Also
note that any external, additional syslog daemons receive their log
data from the journal, too, hence this is the option to use when
logging shall be processed with such a daemon.)

kmsg connects standard output with the kernel log buffer which is
accessible via dmesg(1), in addition to the journal. The journal
daemon might be configured to send all logs to kmsg anyway, in which
case this option is no different from journal.

journal+console and kmsg+console work in a similar way as the two
options above but copy the output to the system console as well.

The file:path option may be used to connect a specific file system
object to standard output. The semantics are similar to the same
option of StandardInput=, see above. If path refers to a regular
file on the filesystem, it is opened (created if it does not exist
yet using privileges of the user executing the systemd process) for
writing at the beginning of the file, but without truncating it. If
standard input and output are directed to the same file path, it is
opened only once — for reading as well as writing — and duplicated.
This is particularly useful when the specified path refers to an
AF_UNIX socket in the file system, as in that case only a single
stream connection is created for both input and output.

append:path is similar to file:path above, but it opens the file in
append mode.

truncate:path is similar to file:path above, but it truncates the
file when opening it. For units with multiple command lines, e.g.
Type=oneshot services with multiple ExecStart=, or services with
ExecCondition=, ExecStartPre= or ExecStartPost=, the output file is
reopened and therefore re-truncated for each command line. If the
output file is truncated while another process still has the file
open, e.g. by an ExecReload= running concurrently with an
ExecStart=, and the other process continues writing to the file
without adjusting its offset, then the space between the file
pointers of the two processes may be filled with NUL bytes,
producing a sparse file. Thus, truncate:path is typically only
useful for units where only one process runs at a time, such as
services with a single ExecStart= and no ExecStartPost=,
ExecReload=, ExecStop= or similar.

socket connects standard output to a socket acquired via socket
activation. The semantics are similar to the same option of
StandardInput=, see above.

The fd:name option connects standard output to a specific, named
file descriptor provided by a socket unit. A name may be specified
as part of this option, following a ":" character (e.g.
"fd:foobar"). If no name is specified, the name "stdout" is implied
(i.e. "fd" is equivalent to "fd:stdout"). At least one socket unit
defining the specified name must be provided via the Sockets=
option, and the file descriptor name may differ from the name of its
containing socket unit. If multiple matches are found, the first one
will be used. See FileDescriptorName= in systemd.socket(5) for more
details about named descriptors and their ordering.

If the standard output (or error output, see below) of a unit is
connected to the journal or the kernel log buffer, the unit will
implicitly gain a dependency of type After= on
systemd-journald.socket (also see the "Implicit Dependencies"
section above). Also note that in this case stdout (or stderr, see
below) will be an AF_UNIX stream socket, and not a pipe or FIFO that
can be reopened. This means when executing shell scripts the
construct echo "hello" > /dev/stderr for writing text to stderr will
not work. To mitigate this use the construct echo "hello" >&2
instead, which is mostly equivalent and avoids this pitfall.

If StandardInput= is set to one of tty, tty-force, tty-fail, socket,
or fd:name, this setting defaults to inherit.

In other cases, this setting defaults to the value set with
DefaultStandardOutput= in systemd-system.conf(5), which defaults to
journal. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).

StandardError=
Controls where file descriptor 2 (stderr) of the executed processes
is connected to. The available options are identical to those of
StandardOutput=, with some exceptions: if set to inherit the file
descriptor used for standard output is duplicated for standard
error, while fd:name will use a default file descriptor name of
"stderr".

This setting defaults to the value set with DefaultStandardError= in
systemd-system.conf(5), which defaults to inherit. Note that setting
this parameter might result in additional dependencies to be added
to the unit (see above).

StandardInputText=, StandardInputData=
Configures arbitrary textual or binary data to pass via file
descriptor 0 (STDIN) to the executed processes. These settings have
no effect unless StandardInput= is set to data (which is the default
if StandardInput= is not set otherwise, but
StandardInputText=/StandardInputData= is). Use this option to embed
process input data directly in the unit file.

StandardInputText= accepts arbitrary textual data. C-style escapes
for special characters as well as the usual "%"-specifiers are
resolved. Each time this setting is used the specified text is
appended to the per-unit data buffer, followed by a newline
character (thus every use appends a new line to the end of the
buffer). Note that leading and trailing whitespace of lines
configured with this option is removed. If an empty line is
specified the buffer is cleared (hence, in order to insert an empty
line, add an additional "\n" to the end or beginning of a line).

StandardInputData= accepts arbitrary binary data, encoded in
Base64[15]. No escape sequences or specifiers are resolved. Any
whitespace in the encoded version is ignored during decoding.

Note that StandardInputText= and StandardInputData= operate on the
same data buffer, and may be mixed in order to configure both binary
and textual data for the same input stream. The textual or binary
data is joined strictly in the order the settings appear in the unit
file. Assigning an empty string to either will reset the data
buffer.

Please keep in mind that in order to maintain readability long unit
file settings may be split into multiple lines, by suffixing each
line (except for the last) with a "\" character (see systemd.unit(5)
for details). This is particularly useful for large data configured
with these two options. Example:

...
StandardInput=data
StandardInputData=V2XigLJyZSBubyBzdHJhbmdlcnMgdG8gbG92ZQpZb3Uga25vdyB0aGUgcnVsZXMgYW5kIHNvIGRv \
IEkKQSBmdWxsIGNvbW1pdG1lbnQncyB3aGF0IEnigLJtIHRoaW5raW5nIG9mCllvdSB3b3VsZG4n \
dCBnZXQgdGhpcyBmcm9tIGFueSBvdGhlciBndXkKSSBqdXN0IHdhbm5hIHRlbGwgeW91IGhvdyBJ \
J20gZmVlbGluZwpHb3R0YSBtYWtlIHlvdSB1bmRlcnN0YW5kCgpOZXZlciBnb25uYSBnaXZlIHlv \
dSB1cApOZXZlciBnb25uYSBsZXQgeW91IGRvd24KTmV2ZXIgZ29ubmEgcnVuIGFyb3VuZCBhbmQg \
ZGVzZXJ0IHlvdQpOZXZlciBnb25uYSBtYWtlIHlvdSBjcnkKTmV2ZXIgZ29ubmEgc2F5IGdvb2Ri \
eWUKTmV2ZXIgZ29ubmEgdGVsbCBhIGxpZSBhbmQgaHVydCB5b3UK
...

Added in version 236.

LogLevelMax=
Configures filtering by log level of log messages generated by this
unit. Takes a syslog log level, one of emerg (lowest log level, only
highest priority messages), alert, crit, err, warning, notice, info,
debug (highest log level, also lowest priority messages). See
syslog(3) for details. By default no filtering is applied (i.e. the
default maximum log level is debug). Use this option to configure
the logging system to drop log messages of a specific service above
the specified level. For example, set LogLevelMax=info in order to
turn off debug logging of a particularly chatty unit. Note that the
configured level is applied to any log messages written by any of
the processes belonging to this unit, as well as any log messages
written by the system manager process (PID 1) in reference to this
unit, sent via any supported logging protocol. The filtering is
applied early in the logging pipeline, before any kind of further
processing is done. Moreover, messages which pass through this
filter successfully might still be dropped by filters applied at a
later stage in the logging subsystem. For example, MaxLevelStore=
configured in journald.conf(5) might prohibit messages of higher log
levels to be stored on disk, even though the per-unit LogLevelMax=
permitted it to be processed.

Added in version 236.

LogExtraFields=
Configures additional log metadata fields to include in all log
records generated by processes associated with this unit, including
systemd. This setting takes one or more journal field assignments in
the format "FIELD=VALUE" separated by whitespace. See
systemd.journal-fields(7) for details on the journal field concept.
Even though the underlying journal implementation permits binary
field values, this setting accepts only valid UTF-8 values. To
include space characters in a journal field value, enclose the
assignment in double quotes ("). The usual specifiers are expanded
in all assignments (see below). Note that this setting is not only
useful for attaching additional metadata to log records of a unit,
but given that all fields and values are indexed may also be used to
implement cross-unit log record matching. Assign an empty string to
reset the list.

Note that this functionality is currently only available in system
services, not in per-user services.

Added in version 236.

LogRateLimitIntervalSec=, LogRateLimitBurst=
Configures the rate limiting that is applied to log messages
generated by this unit. If, in the time interval defined by
LogRateLimitIntervalSec=, more messages than specified in
LogRateLimitBurst= are logged by a service, all further messages
within the interval are dropped until the interval is over. A
message about the number of dropped messages is generated. The time
specification for LogRateLimitIntervalSec= may be specified in the
following units: "s", "min", "h", "ms", "us". See systemd.time(7)
for details. The default settings are set by RateLimitIntervalSec=
and RateLimitBurst= configured in journald.conf(5). Note that this
only applies to log messages that are processed by the logging
subsystem, i.e. by systemd-journald.service(8). This means that if
you connect a service's stderr directly to a file via
StandardOutput=file:... or a similar setting, the rate limiting
will not be applied to messages written that way (but it will be
enforced for messages generated via syslog(3) and similar
functions).

Added in version 240.

LogFilterPatterns=
Define an extended regular expression to filter log messages based
on the MESSAGE= field of the structured message. If the first
character of the pattern is "~", log entries matching the pattern
should be discarded. This option takes a single pattern as an
argument but can be used multiple times to create a list of allowed
and denied patterns. If the empty string is assigned, the filter is
reset, and all prior assignments will have no effect.

Because the "~" character is used to define denied patterns, it must
be replaced with "\x7e" to allow a message starting with "~". For
example, "~foobar" would add a pattern matching "foobar" to the deny
list, while "\x7efoobar" would add a pattern matching "~foobar" to
the allow list.

Log messages are tested against denied patterns (if any), then
against allowed patterns (if any). If a log message matches any of
the denied patterns, it is discarded immediately without considering
allowed patterns. Remaining log messages are tested against allowed
patterns. Messages matching against none of the allowed pattern are
discarded. If no allowed patterns are defined, then all messages are
processed directly after going through denied filters.

Filtering is based on the unit for which LogFilterPatterns= is
defined, meaning log messages coming from systemd(1) about the unit
are not taken into account. Filtered log messages will not be
forwarded to traditional syslog daemons, the kernel log buffer
(kmsg), the systemd console, or sent as wall messages to all
logged-in users.

Note that this functionality is currently only available in system
services, not in per-user services.

Added in version 253.

LogNamespace=
Run the unit's processes in the specified journal namespace. Expects
a short user-defined string identifying the namespace. If not used
the processes of the service are run in the default journal
namespace, i.e. their log stream is collected and processed by
systemd-journald.service. If this option is used any log data
generated by processes of this unit (regardless if via the syslog(),
journal native logging or stdout/stderr logging) is collected and
processed by an instance of the systemd-journald@.service template
unit, which manages the specified namespace. The log data is stored
in a data store independent from the default log namespace's data
store. See systemd-journald.service(8) for details about journal
namespaces.

Internally, journal namespaces are implemented through Linux mount
namespacing and over-mounting the directory that contains the
relevant AF_UNIX sockets used for logging in the unit's mount
namespace. Since mount namespaces are used this setting disconnects
propagation of mounts from the unit's processes to the host,
similarly to how ReadOnlyPaths= and similar settings describe above
work. Journal namespaces may hence not be used for services that
need to establish mount points on the host.

When this option is used the unit will automatically gain ordering
and requirement dependencies on the two socket units associated with
the systemd-journald@.service instance so that they are
automatically established prior to the unit starting up. Note that
when this option is used log output of this service does not appear
in the regular journalctl(1) output, unless the --namespace= option
is used.

This option is only available for system services and is not
supported for services running in per-user instances of the service
manager.

Added in version 245.

SyslogIdentifier=
Sets the process name ("syslog tag") to prefix log lines sent to the
logging system or the kernel log buffer with. If not set, defaults
to the process name of the executed process. This option is only
useful when StandardOutput= or StandardError= are set to journal or
kmsg (or to the same settings in combination with +console) and only
applies to log messages written to stdout or stderr.

SyslogFacility=
Sets the syslog facility identifier to use when logging. One of
kern, user, mail, daemon, auth, syslog, lpr, news, uucp, cron,
authpriv, ftp, local0, local1, local2, local3, local4, local5,
local6 or local7. See syslog(3) for details. This option is only
useful when StandardOutput= or StandardError= are set to journal or
kmsg (or to the same settings in combination with +console), and
only applies to log messages written to stdout or stderr. Defaults
to daemon.

SyslogLevel=
The default syslog log level to use when logging to the logging
system or the kernel log buffer. One of emerg, alert, crit, err,
warning, notice, info, debug. See syslog(3) for details. This option
is only useful when StandardOutput= or StandardError= are set to
journal or kmsg (or to the same settings in combination with
+console), and only applies to log messages written to stdout or
stderr. Note that individual lines output by executed processes may
be prefixed with a different log level which can be used to override
the default log level specified here. The interpretation of these
prefixes may be disabled with SyslogLevelPrefix=, see below. For
details, see sd-daemon(3). Defaults to info.

SyslogLevelPrefix=
Takes a boolean argument. If true and StandardOutput= or
StandardError= are set to journal or kmsg (or to the same settings
in combination with +console), log lines written by the executed
process that are prefixed with a log level will be processed with
this log level set but the prefix removed. If set to false, the
interpretation of these prefixes is disabled and the logged lines
are passed on as-is. This only applies to log messages written to
stdout or stderr. For details about this prefixing see sd-daemon(3).
Defaults to true.

TTYPath=
Sets the terminal device node to use if standard input, output, or
error are connected to a TTY (see above). Defaults to /dev/console.

TTYReset=
Reset the terminal device specified with TTYPath= before and after
execution. This does not erase the screen (see TTYVTDisallocate=
below for that). Defaults to "no".

TTYVHangup=
Disconnect all clients which have opened the terminal device
specified with TTYPath= before and after execution. Defaults to
"no".

TTYColumns=, TTYRows=
Configure the size of the TTY specified with TTYPath=. If unset or
set to the empty string, it is attempted to retrieve the dimensions
of the terminal screen via ANSI sequences, and if that fails the
kernel defaults (typically 80x24) are used.

Added in version 250.

TTYVTDisallocate=
If the terminal device specified with TTYPath= is a virtual console
terminal, try to deallocate the TTY before and after execution. This
ensures that the screen and scrollback buffer is cleared. If the
terminal device is of any other type of TTY an attempt is made to
clear the screen via ANSI sequences. Defaults to "no".

CREDENTIALS
LoadCredential=ID[:PATH], LoadCredentialEncrypted=ID[:PATH]
Pass a credential to the unit. Credentials are limited-size binary
or textual objects that may be passed to unit processes. They are
primarily used for passing cryptographic keys (both public and
private) or certificates, user account information or identity
information from host to services. The data is accessible from the
unit's processes via the file system, at a read-only location that
(if possible and permitted) is backed by non-swappable memory. The
data is only accessible to the user associated with the unit, via
the User=/DynamicUser= settings (as well as the superuser). When
available, the location of credentials is exported as the
$CREDENTIALS_DIRECTORY environment variable to the unit's processes.

The LoadCredential= setting takes a textual ID to use as name for a
credential plus a file system path, separated by a colon. The ID
must be a short ASCII string suitable as filename in the filesystem,
and may be chosen freely by the user. If the specified path is
absolute it is opened as regular file and the credential data is
read from it. If the absolute path refers to an AF_UNIX stream
socket in the file system a connection is made to it (only once at
unit start-up) and the credential data read from the connection,
providing an easy IPC integration point for dynamically transferring
credentials from other services.

If the specified path is not absolute and itself qualifies as valid
credential identifier it is attempted to find a credential that the
service manager itself received under the specified name — which may
be used to propagate credentials from an invoking environment (e.g.
a container manager that invoked the service manager) into a
service. If no matching system credential is found, the directories
/etc/credstore/, /run/credstore/ and /usr/lib/credstore/ are
searched for files under the credential's name — which hence are
recommended locations for credential data on disk. If
LoadCredentialEncrypted= is used /run/credstore.encrypted/,
/etc/credstore.encrypted/, and /usr/lib/credstore.encrypted/ are
searched as well.

If the file system path is omitted it is chosen identical to the
credential name, i.e. this is a terse way to declare credentials to
inherit from the service manager into a service. This option may be
used multiple times, each time defining an additional credential to
pass to the unit.

Note that if the path is not specified or a valid credential
identifier is given, i.e. in the above two cases, a missing
credential is not considered fatal.

If an absolute path referring to a directory is specified, every
file in that directory (recursively) will be loaded as a separate
credential. The ID for each credential will be the provided ID
suffixed with "_$FILENAME" (e.g., "Key_file1"). When loading from a
directory, symlinks will be ignored.

The contents of the file/socket may be arbitrary binary or textual
data, including newline characters and NUL bytes.

The LoadCredentialEncrypted= setting is identical to
LoadCredential=, except that the credential data is decrypted and
authenticated before being passed on to the executed processes.
Specifically, the referenced path should refer to a file or socket
with an encrypted credential, as implemented by systemd-creds(1).
This credential is loaded, decrypted, authenticated and then passed
to the application in plaintext form, in the same way a regular
credential specified via LoadCredential= would be. A credential
configured this way may be symmetrically encrypted/authenticated
with a secret key derived from the system's TPM2 security chip, or
with a secret key stored in /var/lib/systemd/credentials.secret, or
with both. Using encrypted and authenticated credentials improves
security as credentials are not stored in plaintext and only
authenticated and decrypted into plaintext the moment a service
requiring them is started. Moreover, credentials may be bound to the
local hardware and installations, so that they cannot easily be
analyzed offline, or be generated externally. When DevicePolicy= is
set to "closed" or "strict", or set to "auto" and DeviceAllow= is
set, or PrivateDevices= is set, then this setting adds /dev/tpmrm0
with rw mode to DeviceAllow=. See systemd.resource-control(5) for
the details about DevicePolicy= or DeviceAllow=.

Note that encrypted credentials targeted for services of the
per-user service manager must be encrypted with systemd-creds
encrypt --user, and those for the system service manager without the
--user switch. Encrypted credentials are always targeted to a
specific user or the system as a whole, and it is ensured that
per-user service managers cannot decrypt secrets intended for the
system or for other users.

The credential files/IPC sockets must be accessible to the service
manager, but do not have to be directly accessible to the unit's
processes: the credential data is read and copied into separate,
read-only copies for the unit that are accessible to appropriately
privileged processes. This is particularly useful in combination
with DynamicUser= as this way privileged data can be made available
to processes running under a dynamic UID (i.e. not a previously
known one) without having to open up access to all users.

In order to reference the path a credential may be read from within
a ExecStart= command line use "${CREDENTIALS_DIRECTORY}/mycred",
e.g. "ExecStart=cat ${CREDENTIALS_DIRECTORY}/mycred". In order to
reference the path a credential may be read from within a
Environment= line use "%d/mycred", e.g.
"Environment=MYCREDPATH=%d/mycred". For system services the path may
also be referenced as "/run/credentials/UNITNAME" in cases where no
interpolation is possible, e.g. configuration files of software that
does not yet support credentials natively. $CREDENTIALS_DIRECTORY
is considered the primary interface to look for credentials, though,
since it also works for user services.

Currently, an accumulated credential size limit of 1 MB per unit is
enforced.

The service manager itself may receive system credentials that can
be propagated to services from a hosting container manager or VM
hypervisor. See the Container Interface[16] documentation for
details about the former. For the latter, pass DMI/SMBIOS[17] OEM
string table entries (field type 11) with a prefix of
"io.systemd.credential:" or "io.systemd.credential.binary:". In both
cases a key/value pair separated by "=" is expected, in the latter
case the right-hand side is Base64 decoded when parsed (thus
permitting binary data to be passed in). Example qemu[18] switch:
"-smbios type=11,value=io.systemd.credential:xx=yy", or "-smbios
type=11,value=io.systemd.credential.binary:rick=TmV2ZXIgR29ubmEgR2l2ZSBZb3UgVXA=".
Alternatively, use the qemu "fw_cfg" node
"opt/io.systemd.credentials/". Example qemu switch: "-fw_cfg
name=opt/io.systemd.credentials/mycred,string=supersecret". They may
also be passed from the UEFI firmware environment via systemd-
stub(7), from the initrd (see systemd(1)), or be specified on the
kernel command line using the "systemd.set_credential=" and
"systemd.set_credential_binary=" switches (see systemd(1) – this is
not recommended since unprivileged userspace can read the kernel
command line).

If referencing an AF_UNIX stream socket to connect to, the
connection will originate from an abstract namespace socket, that
includes information about the unit and the credential ID in its
socket name. Use getpeername(2) to query this information. The
returned socket name is formatted as NUL RANDOM "/unit/" UNIT "/"
ID, i.e. a NUL byte (as required for abstract namespace socket
names), followed by a random string (consisting of alphadecimal
characters), followed by the literal string "/unit/", followed by
the requesting unit name, followed by the literal character "/",
followed by the textual credential ID requested. Example:
"\0adf9d86b6eda275e/unit/foobar.service/credx" in case the
credential "credx" is requested for a unit "foobar.service". This
functionality is useful for using a single listening socket to serve
credentials to multiple consumers.

For further information see System and Service Credentials[19]
documentation.

Added in version 247.

ImportCredential=GLOB
Pass one or more credentials to the unit. Takes a credential name
for which we will attempt to find a credential that the service
manager itself received under the specified name — which may be used
to propagate credentials from an invoking environment (e.g. a
container manager that invoked the service manager) into a service.
If the credential name is a glob, all credentials matching the glob
are passed to the unit. Matching credentials are searched for in the
system credentials, the encrypted system credentials, and under
/etc/credstore/, /run/credstore/, /usr/lib/credstore/,
/run/credstore.encrypted/, /etc/credstore.encrypted/, and
/usr/lib/credstore.encrypted/ in that order. When multiple
credentials of the same name are found, the first one found is used.

The globbing expression implements a restrictive subset of glob(7):
only a single trailing "*" wildcard may be specified. Both "?" and
"[]" wildcards are not permitted, nor are "*" wildcards anywhere
except at the end of the glob expression.

Optionally, the credential name or glob may be followed by a colon
followed by a rename pattern. If specified, all credentials matching
the credential name or glob are renamed according to the given
pattern. For example, if
"ImportCredential=my.original.cred:my.renamed.cred" is specified,
the service manager will read the "my.original.cred" credential and
make it available as the "my.renamed.cred" credential to the
service. Similarly, if "ImportCredential=my.original.*:my.renamed."
is specified, the service manager will read all credentials starting
with "my.original." and make them available as "my.renamed.xxx" to
the service.

If ImportCredential= is specified multiple times and multiple
credentials end up with the same name after renaming, the first one
is kept and later ones are dropped.

When multiple credentials of the same name are found, credentials
found by LoadCredential= and LoadCredentialEncrypted= take priority
over credentials found by ImportCredential=.

Added in version 254.

SetCredential=ID:VALUE, SetCredentialEncrypted=ID:VALUE
The SetCredential= setting is similar to LoadCredential= but accepts
a literal value to use as data for the credential, instead of a file
system path to read the data from. Do not use this option for data
that is supposed to be secret, as it is accessible to unprivileged
processes via IPC. It's only safe to use this for user IDs, public
key material and similar non-sensitive data. For everything else use
LoadCredential=. In order to embed binary data into the credential
data use C-style escaping (i.e. "\n" to embed a newline, or "\x00"
to embed a NUL byte).

The SetCredentialEncrypted= setting is identical to SetCredential=
but expects an encrypted credential in literal form as value. This
allows embedding confidential credentials securely directly in unit
files. Use systemd-creds(1)' -p switch to generate suitable
SetCredentialEncrypted= lines directly from plaintext credentials.
For further details see LoadCredentialEncrypted= above.

When multiple credentials of the same name are found, credentials
found by LoadCredential=, LoadCredentialEncrypted= and
ImportCredential= take priority over credentials found by
SetCredential=. As such, SetCredential= will act as default if no
credentials are found by any of the former. In this case not being
able to retrieve the credential from the path specified in
LoadCredential= or LoadCredentialEncrypted= is not considered fatal.

Added in version 247.

SYSTEM V COMPATIBILITY
UtmpIdentifier=
Takes a four character identifier string for an utmp(5) and wtmp
entry for this service. This should only be set for services such as
getty implementations (such as agetty(8)) where utmp/wtmp entries
must be created and cleared before and after execution, or for
services that shall be executed as if they were run by a getty
process (see below). If the configured string is longer than four
characters, it is truncated and the terminal four characters are
used. This setting interprets %I style string replacements. This
setting is unset by default, i.e. no utmp/wtmp entries are created
or cleaned up for this service.

UtmpMode=
Takes one of "init", "login" or "user". If UtmpIdentifier= is set,
controls which type of utmp(5)/wtmp entries for this service are
generated. This setting has no effect unless UtmpIdentifier= is set
too. If "init" is set, only an INIT_PROCESS entry is generated and
the invoked process must implement a getty-compatible utmp/wtmp
logic. If "login" is set, first an INIT_PROCESS entry, followed by a
LOGIN_PROCESS entry is generated. In this case, the invoked process
must implement a login(1)-compatible utmp/wtmp logic. If "user" is
set, first an INIT_PROCESS entry, then a LOGIN_PROCESS entry and
finally a USER_PROCESS entry is generated. In this case, the invoked
process may be any process that is suitable to be run as session
leader. Defaults to "init".

Added in version 225.

ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
Processes started by the service manager are executed with an
environment variable block assembled from multiple sources. Processes
started by the system service manager generally do not inherit
environment variables set for the service manager itself (but this may
be altered via PassEnvironment=), but processes started by the user
service manager instances generally do inherit all environment variables
set for the service manager itself.

For each invoked process the list of environment variables set is
compiled from the following sources:

• Variables globally configured for the service manager, using the
DefaultEnvironment= setting in systemd-system.conf(5), the kernel
command line option systemd.setenv= understood by systemd(1), or via
systemctl(1) set-environment verb.

• Variables defined by the service manager itself (see the list
below).

• Variables set in the service manager's own environment variable
block (subject to PassEnvironment= for the system service manager).

• Variables set via Environment= in the unit file.

• Variables read from files specified via EnvironmentFile= in the unit
file.

• Variables set by any PAM modules in case PAMName= is in effect,
cf. pam_env(8).

If the same environment variable is set by multiple of these sources,
the later source — according to the order of the list above — wins. Note
that as the final step all variables listed in UnsetEnvironment= are
removed from the compiled environment variable list, immediately before
it is passed to the executed process.

The general philosophy is to expose a small curated list of environment
variables to processes. Services started by the system manager (PID 1)
will be started, without additional service-specific configuration, with
just a few environment variables. The user manager inherits environment
variables as any other system service, but in addition may receive
additional environment variables from PAM, and, typically, additional
imported variables when the user starts a graphical session. It is
recommended to keep the environment blocks in both the system and user
managers lean. Importing all variables inherited by the graphical
session or by one of the user shells is strongly discouraged.

Hint: systemd-run -P env and systemd-run --user -P env print the
effective system and user service environment blocks.

Environment Variables Set or Propagated by the Service Manager
The following environment variables are propagated by the service
manager or generated internally for each invoked process:

$PATH
Colon-separated list of directories to use when launching
executables. systemd uses a fixed value of
"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the system
manager. In case of the user manager, a different path may be
configured by the distribution. It is recommended to not rely on the
order of entries, and have only one program with a given name in
$PATH.

Added in version 208.

$LANG
Locale. Can be set in locale.conf(5) or on the kernel command line
(see systemd(1) and kernel-command-line(7)).

Added in version 208.

$USER, $LOGNAME, $HOME, $SHELL
User name (twice), home directory, and the login shell. $USER is
set unconditionally, while $HOME, $LOGNAME, and $SHELL are only set
for the units that have User= set and SetLoginEnvironment= unset or
set to true. For user services, these variables are typically
inherited from the user manager itself. See passwd(5).

Added in version 208.

$INVOCATION_ID
Contains a randomized, unique 128-bit ID identifying each runtime
cycle of the unit, formatted as 32 character hexadecimal string. A
new ID is assigned each time the unit changes from an inactive state
into an activating or active state, and may be used to identify this
specific runtime cycle, in particular in data stored offline, such
as the journal. The same ID is passed to all processes run as part
of the unit.

Added in version 232.

$XDG_RUNTIME_DIR
The directory to use for runtime objects (such as IPC objects) and
volatile state. Set for all services run by the user systemd
instance, as well as any system services that use PAMName= with a
PAM stack that includes pam_systemd. See below and pam_systemd(8)
for more information.

Added in version 208.

$RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY, $LOGS_DIRECTORY,
$CONFIGURATION_DIRECTORY
Absolute paths to the directories defined with RuntimeDirectory=,
StateDirectory=, CacheDirectory=, LogsDirectory=, and
ConfigurationDirectory= when those settings are used.

Added in version 244.

$CREDENTIALS_DIRECTORY
An absolute path to the per-unit directory with credentials
configured via ImportCredential=/LoadCredential=/SetCredential=. The
directory is marked read-only and is placed in unswappable memory
(if supported and permitted), and is only accessible to the UID
associated with the unit via User= or DynamicUser= (and the
superuser).

Added in version 247.

$MAINPID
The PID of the unit's main process if it is known. This is only set
for control processes as invoked by ExecReload= and similar.

Added in version 209.

$MANAGERPID
The PID of the user systemd instance, set for processes spawned by
it.

Added in version 208.

$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
Information about file descriptors passed to a service for socket
activation. See sd_listen_fds(3).

Added in version 208.

$NOTIFY_SOCKET
The socket sd_notify() talks to. See sd_notify(3).

Added in version 229.

$WATCHDOG_PID, $WATCHDOG_USEC
Information about watchdog keep-alive notifications. See
sd_watchdog_enabled(3).

Added in version 229.

$SYSTEMD_EXEC_PID
The PID of the unit process (e.g. process invoked by ExecStart=).
The child process can use this information to determine whether the
process is directly invoked by the service manager or indirectly as
a child of another process by comparing this value with the current
PID (similarly to the scheme used in sd_listen_fds(3) with
$LISTEN_PID and $LISTEN_FDS).

Added in version 248.

$TERM
Terminal type, set only for units connected to a terminal
(StandardInput=tty, StandardOutput=tty, or StandardError=tty). See
termcap(5).

Added in version 209.

$LOG_NAMESPACE
Contains the name of the selected logging namespace when the
LogNamespace= service setting is used.

Added in version 246.

$JOURNAL_STREAM
If the standard output or standard error output of the executed
processes are connected to the journal (for example, by setting
StandardError=journal) $JOURNAL_STREAM contains the device and inode
numbers of the connection file descriptor, formatted in decimal,
separated by a colon (":"). This permits invoked processes to safely
detect whether their standard output or standard error output are
connected to the journal. The device and inode numbers of the file
descriptors should be compared with the values set in the
environment variable to determine whether the process output is
still connected to the journal. Note that it is generally not
sufficient to only check whether $JOURNAL_STREAM is set at all as
services might invoke external processes replacing their standard
output or standard error output, without unsetting the environment
variable.

If both standard output and standard error of the executed processes
are connected to the journal via a stream socket, this environment
variable will contain information about the standard error stream,
as that's usually the preferred destination for log data. (Note that
typically the same stream is used for both standard output and
standard error, hence very likely the environment variable contains
device and inode information matching both stream file descriptors.)

This environment variable is primarily useful to allow services to
optionally upgrade their used log protocol to the native journal
protocol (using sd_journal_print(3) and other functions) if their
standard output or standard error output is connected to the journal
anyway, thus enabling delivery of structured metadata along with
logged messages.

Added in version 231.

$SERVICE_RESULT
Only used for the service unit type. This environment variable is
passed to all ExecStop= and ExecStopPost= processes, and encodes the
service "result". Currently, the following values are defined:

Table 5. Defined $SERVICE_RESULT values
┌───────────────────┬────────────────────────────┐
│ Value │ Meaning │
├───────────────────┼────────────────────────────┤
│ "success" │ The service ran │
│ │ successfully and exited │
│ │ cleanly. │
├───────────────────┼────────────────────────────┤
│ "protocol" │ A protocol violation │
│ │ occurred: the service did │
│ │ not take the steps │
│ │ required by its unit │
│ │ configuration │
│ │ (specifically what is │
│ │ configured in its Type= │
│ │ setting). │
├───────────────────┼────────────────────────────┤
│ "timeout" │ One of the steps timed │
│ │ out. │
├───────────────────┼────────────────────────────┤
│ "exit-code" │ Service process exited │
│ │ with a non-zero exit code; │
│ │ see $EXIT_CODE below for │
│ │ the actual exit code │
│ │ returned. │
├───────────────────┼────────────────────────────┤
│ "signal" │ A service process was │
│ │ terminated abnormally by a │
│ │ signal, without dumping │
│ │ core. See $EXIT_CODE below │
│ │ for the actual signal │
│ │ causing the termination. │
├───────────────────┼────────────────────────────┤
│ "core-dump" │ A service process │
│ │ terminated abnormally with │
│ │ a signal and dumped core. │
│ │ See $EXIT_CODE below for │
│ │ the signal causing the │
│ │ termination. │
├───────────────────┼────────────────────────────┤
│ "watchdog" │ Watchdog keep-alive ping │
│ │ was enabled for the │
│ │ service, but the deadline │
│ │ was missed. │
├───────────────────┼────────────────────────────┤
│ "exec-condition" │ Service did not run │
│ │ because ExecCondition= │
│ │ failed. │
├───────────────────┼────────────────────────────┤
│ "oom-kill" │ A service process was │
│ │ terminated by the │
│ │ Out-Of-Memory (OOM) │
│ │ killer. │
├───────────────────┼────────────────────────────┤
│ "start-limit-hit" │ A start limit was defined │
│ │ for the unit and it was │
│ │ hit, causing the unit to │
│ │ fail to start. See │
│ │ systemd.unit(5)'s │
│ │ StartLimitIntervalSec= and │
│ │ StartLimitBurst= for │
│ │ details. │
├───────────────────┼────────────────────────────┤
│ "resources" │ A catch-all condition in │
│ │ case a system operation │
│ │ failed. │
└───────────────────┴────────────────────────────┘

This environment variable is useful to monitor failure or successful
termination of a service. Even though this variable is available in
both ExecStop= and ExecStopPost=, it is usually a better choice to
place monitoring tools in the latter, as the former is only invoked
for services that managed to start up correctly, and the latter
covers both services that failed during their start-up and those
which failed during their runtime.

Added in version 232.

$EXIT_CODE, $EXIT_STATUS
Only defined for the service unit type. These environment variables
are passed to all ExecStop=, ExecStopPost= processes and contain
exit status/code information of the main process of the service. For
the precise definition of the exit code and status, see wait(2).
$EXIT_CODE is one of "exited", "killed", "dumped". $EXIT_STATUS
contains the numeric exit code formatted as string if $EXIT_CODE is
"exited", and the signal name in all other cases. Note that these
environment variables are only set if the service manager succeeded
to start and identify the main process of the service.

Table 6. Summary of possible service result variable values
┌───────────────────┬──────────────────┬─────────────────────┐
│ $SERVICE_RESULT │ $EXIT_CODE │ $EXIT_STATUS │
├───────────────────┼──────────────────┼─────────────────────┤
│ "success" │ "killed" │ "HUP", "INT", │
│ │ │ "TERM", "PIPE" │
│ ├──────────────────┼─────────────────────┤
│ │ "exited" │ "0" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "protocol" │ not set │ not set │
│ ├──────────────────┼─────────────────────┤
│ │ "exited" │ "0" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "timeout" │ "killed" │ "TERM", "KILL" │
│ ├──────────────────┼─────────────────────┤
│ │ "exited" │ "0", "1", "2", "3", │
│ │ │ ..., "255" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "exit-code" │ "exited" │ "1", "2", "3", ..., │
│ │ │ "255" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "signal" │ "killed" │ "HUP", "INT", │
│ │ │ "KILL", ... │
├───────────────────┼──────────────────┼─────────────────────┤
│ "core-dump" │ "dumped" │ "ABRT", "SEGV", │
│ │ │ "QUIT", ... │
├───────────────────┼──────────────────┼─────────────────────┤
│ "watchdog" │ "dumped" │ "ABRT" │
│ ├──────────────────┼─────────────────────┤
│ │ "killed" │ "TERM", "KILL" │
│ ├──────────────────┼─────────────────────┤
│ │ "exited" │ "0", "1", "2", "3", │
│ │ │ ..., "255" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "exec-condition" │ "exited" │ "1", "2", "3", "4", │
│ │ │ ..., "254" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "oom-kill" │ "killed" │ "TERM", "KILL" │
├───────────────────┼──────────────────┼─────────────────────┤
│ "start-limit-hit" │ not set │ not set │
├───────────────────┼──────────────────┼─────────────────────┤
│ "resources" │ any of the above │ any of the above │
├───────────────────┴──────────────────┴─────────────────────┤
│ Note: the process may be also terminated by a signal not │
│ sent by systemd. In particular the process may send an │
│ arbitrary signal to itself in a handler for any of the │
│ non-maskable signals. Nevertheless, in the "timeout" and │
│ "watchdog" rows above only the signals that systemd sends │
│ have been included. Moreover, using SuccessExitStatus= │
│ additional exit statuses may be declared to indicate clean │
│ termination, which is not reflected by this table. │
└────────────────────────────────────────────────────────────┘

Added in version 232.

$MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE, $MONITOR_EXIT_STATUS,
$MONITOR_INVOCATION_ID, $MONITOR_UNIT
Only defined for the service unit type. Those environment variables
are passed to all ExecStart= and ExecStartPre= processes which run
in services triggered by OnFailure= or OnSuccess= dependencies.

Variables $MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE and
$MONITOR_EXIT_STATUS take the same values as for ExecStop= and
ExecStopPost= processes. Variables $MONITOR_INVOCATION_ID and
$MONITOR_UNIT are set to the invocation id and unit name of the
service which triggered the dependency.

Note that when multiple services specify the same unit as their
OnFailure= or OnSuccess= handler, those variables will not be
passed. Consider using a template handler unit for that case
instead: "OnFailure=handler@%n.service" for non-templated units, or
"OnFailure=handler@%p-%i.service" for templated units.

Added in version 251.

$PIDFILE
The path to the configured PID file, in case the process is forked
off on behalf of a service that uses the PIDFile= setting, see
systemd.service(5) for details. Service code may use this
environment variable to automatically generate a PID file at the
location configured in the unit file. This field is set to an
absolute path in the file system.

Added in version 242.

$REMOTE_ADDR, $REMOTE_PORT
If this is a unit started via per-connection socket activation (i.e.
via a socket unit with Accept=yes), these environment variables
contain information about the remote peer of the socket connection.

For IPv4 and IPv6 connections, $REMOTE_ADDR contains the IP address,
and $REMOTE_PORT contains the port number of the remote peer.

For AF_UNIX socket connections, $REMOTE_ADDR contains either the
remote socket's file system path starting with a slash ("/"), its
address in the abstract namespace starting with an at symbol ("@"),
or is unset in case of an unnamed socket. $REMOTE_PORT is not set
for AF_UNIX sockets.

Added in version 220.

$TRIGGER_UNIT, $TRIGGER_PATH, $TRIGGER_TIMER_REALTIME_USEC,
$TRIGGER_TIMER_MONOTONIC_USEC
If the unit was activated dynamically (e.g.: a corresponding path
unit or timer unit), the unit that triggered it and other
type-dependent information will be passed via these variables. Note
that this information is provided in a best-effort way. For example,
multiple triggers happening one after another will be coalesced and
only one will be reported, with no guarantee as to which one it will
be. Because of this, in most cases this variable will be primarily
informational, i.e. useful for debugging purposes, is lossy, and
should not be relied upon to propagate a comprehensive reason for
activation.

Added in version 252.

$MEMORY_PRESSURE_WATCH, $MEMORY_PRESSURE_WRITE
If memory pressure monitoring is enabled for this service unit, the
path to watch and the data to write into it. See Memory Pressure
Handling[20] for details about these variables and the service
protocol data they convey.

Added in version 254.

$FDSTORE
The maximum number of file descriptors that may be stored in the
manager for the service. This variable is set when the file
descriptor store is enabled for the service, i.e.
FileDescriptorStoreMax= is set to a non-zero value (see
systemd.service(5) for details). Applications may check this
environment variable before sending file descriptors to the service
manager via sd_pid_notify_with_fds(3).

Added in version 254.

$DEBUG_INVOCATION
If RestartMode=debug is set, and a previous attempt at starting the
unit failed, this variable will be passed to the service to indicate
that additional logging should be enabled at startup. See
systemd.service(5) for more details.

Added in version 257.

For system services, when PAMName= is enabled and pam_systemd is part of
the selected PAM stack, additional environment variables defined by
systemd may be set for services. Specifically, these are $XDG_SEAT,
$XDG_VTNR, see pam_systemd(8) for details.

PROCESS EXIT CODES
When invoking a unit process the service manager possibly fails to apply
the execution parameters configured with the settings above. In that
case the already created service process will exit with a non-zero exit
code before the configured command line is executed. (Or in other words,
the child process possibly exits with these error codes, after having
been created by the fork(2) system call, but before the matching
execve(2) system call is called.) Specifically, exit codes defined by
the C library, by the LSB specification and by the systemd service
manager itself are used.

The following basic service exit codes are defined by the C library.

Table 7. Basic C library exit codes
┌───────────┬───────────────┬────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼───────────────┼────────────────────┤
│ 0 │ EXIT_SUCCESS │ Generic success │
│ │ │ code. │
├───────────┼───────────────┼────────────────────┤
│ 1 │ EXIT_FAILURE │ Generic failure or │
│ │ │ unspecified error. │
└───────────┴───────────────┴────────────────────┘

The following service exit codes are defined by the LSB
specification[21].

Table 8. LSB service exit codes
┌───────────┬──────────────────────┬────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼──────────────────────┼────────────────────┤
│ 2 │ EXIT_INVALIDARGUMENT │ Invalid or excess │
│ │ │ arguments. │
├───────────┼──────────────────────┼────────────────────┤
│ 3 │ EXIT_NOTIMPLEMENTED │ Unimplemented │
│ │ │ feature. │
├───────────┼──────────────────────┼────────────────────┤
│ 4 │ EXIT_NOPERMISSION │ The user has │
│ │ │ insufficient │
│ │ │ privileges. │
├───────────┼──────────────────────┼────────────────────┤
│ 5 │ EXIT_NOTINSTALLED │ The program is not │
│ │ │ installed. │
├───────────┼──────────────────────┼────────────────────┤
│ 6 │ EXIT_NOTCONFIGURED │ The program is not │
│ │ │ configured. │
├───────────┼──────────────────────┼────────────────────┤
│ 7 │ EXIT_NOTRUNNING │ The program is not │
│ │ │ running. │
└───────────┴──────────────────────┴────────────────────┘

The LSB specification suggests that error codes 200 and above are
reserved for implementations. Some of them are used by the service
manager to indicate problems during process invocation:

Table 9. systemd-specific exit codes
┌───────────┬──────────────────────────────┬─────────────────────────────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 200 │ EXIT_CHDIR │ Changing to the │
│ │ │ requested working │
│ │ │ directory failed. │
│ │ │ See │
│ │ │ WorkingDirectory= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 201 │ EXIT_NICE │ Failed to set up │
│ │ │ process scheduling │
│ │ │ priority (nice │
│ │ │ level). See Nice= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 202 │ EXIT_FDS │ Failed to close │
│ │ │ unwanted file │
│ │ │ descriptors, or to │
│ │ │ adjust passed file │
│ │ │ descriptors. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 203 │ EXIT_EXEC │ The actual process │
│ │ │ execution failed │
│ │ │ (specifically, the │
│ │ │ execve(2) system │
│ │ │ call). Most likely │
│ │ │ this is caused by a │
│ │ │ missing or │
│ │ │ non-accessible │
│ │ │ executable file. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 204 │ EXIT_MEMORY │ Failed to perform an │
│ │ │ action due to memory │
│ │ │ shortage. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 205 │ EXIT_LIMITS │ Failed to adjust │
│ │ │ resource limits. See │
│ │ │ LimitCPU= and │
│ │ │ related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 206 │ EXIT_OOM_ADJUST │ Failed to adjust the │
│ │ │ OOM setting. See │
│ │ │ OOMScoreAdjust= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 207 │ EXIT_SIGNAL_MASK │ Failed to set │
│ │ │ process signal mask. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 208 │ EXIT_STDIN │ Failed to set up │
│ │ │ standard input. See │
│ │ │ StandardInput= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 209 │ EXIT_STDOUT │ Failed to set up │
│ │ │ standard output. See │
│ │ │ StandardOutput= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 210 │ EXIT_CHROOT │ Failed to change │
│ │ │ root directory │
│ │ │ (chroot(2)). See │
│ │ │ RootDirectory=/RootImage= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 211 │ EXIT_IOPRIO │ Failed to set up IO │
│ │ │ scheduling priority. See │
│ │ │ IOSchedulingClass=/IOSchedulingPriority= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 212 │ EXIT_TIMERSLACK │ Failed to set up timer slack. See │
│ │ │ TimerSlackNSec= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 213 │ EXIT_SECUREBITS │ Failed to set process secure bits. See │
│ │ │ SecureBits= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 214 │ EXIT_SETSCHEDULER │ Failed to set up CPU scheduling. See │
│ │ │ CPUSchedulingPolicy=/CPUSchedulingPriority= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 215 │ EXIT_CPUAFFINITY │ Failed to set up CPU affinity. See │
│ │ │ CPUAffinity= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 216 │ EXIT_GROUP │ Failed to determine or change group │
│ │ │ credentials. See │
│ │ │ Group=/SupplementaryGroups= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 217 │ EXIT_USER │ Failed to determine or change user │
│ │ │ credentials, or to set up user namespacing. │
│ │ │ See User=/PrivateUsers= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 218 │ EXIT_CAPABILITIES │ Failed to drop capabilities, or apply │
│ │ │ ambient capabilities. See │
│ │ │ CapabilityBoundingSet=/AmbientCapabilities= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 219 │ EXIT_CGROUP │ Setting up the service control group │
│ │ │ failed. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 220 │ EXIT_SETSID │ Failed to create new process session. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 221 │ EXIT_CONFIRM │ Execution has been cancelled by the user. │
│ │ │ See the systemd.confirm_spawn= kernel │
│ │ │ command line setting on kernel-command- │
│ │ │ line(7) for details. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 222 │ EXIT_STDERR │ Failed to set up standard error output. See │
│ │ │ StandardError= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 224 │ EXIT_PAM │ Failed to set up PAM session. See PAMName= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 225 │ EXIT_NETWORK │ Failed to set up network namespacing. See │
│ │ │ PrivateNetwork= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 226 │ EXIT_NAMESPACE │ Failed to set up mount, UTS, or IPC │
│ │ │ namespacing. See ReadOnlyPaths=, │
│ │ │ ProtectHostname=, PrivateIPC=, and related │
│ │ │ settings above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 227 │ EXIT_NO_NEW_PRIVILEGES │ Failed to disable new privileges. See │
│ │ │ NoNewPrivileges=yes above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 228 │ EXIT_SECCOMP │ Failed to apply system call filters. See │
│ │ │ SystemCallFilter= and related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 229 │ EXIT_SELINUX_CONTEXT │ Determining or changing SELinux context │
│ │ │ failed. See SELinuxContext= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 230 │ EXIT_PERSONALITY │ Failed to set up an execution domain │
│ │ │ (personality). See Personality= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 231 │ EXIT_APPARMOR_PROFILE │ Failed to prepare changing AppArmor │
│ │ │ profile. See AppArmorProfile= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 232 │ EXIT_ADDRESS_FAMILIES │ Failed to restrict address families. See │
│ │ │ RestrictAddressFamilies= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 233 │ EXIT_RUNTIME_DIRECTORY │ Setting up runtime directory failed. See │
│ │ │ RuntimeDirectory= and related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 235 │ EXIT_CHOWN │ Failed to adjust socket ownership. Used for │
│ │ │ socket units only. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 236 │ EXIT_SMACK_PROCESS_LABEL │ Failed to set SMACK label. See │
│ │ │ SmackProcessLabel= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 237 │ EXIT_KEYRING │ Failed to set up kernel keyring. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 238 │ EXIT_STATE_DIRECTORY │ Failed to set up unit's state directory. │
│ │ │ See StateDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 239 │ EXIT_CACHE_DIRECTORY │ Failed to set up unit's cache directory. │
│ │ │ See CacheDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 240 │ EXIT_LOGS_DIRECTORY │ Failed to set up unit's logging directory. │
│ │ │ See LogsDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 241 │ EXIT_CONFIGURATION_DIRECTORY │ Failed to set up unit's configuration │
│ │ │ directory. See ConfigurationDirectory= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 242 │ EXIT_NUMA_POLICY │ Failed to set up unit's NUMA memory policy. │
│ │ │ See NUMAPolicy= and NUMAMask= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 243 │ EXIT_CREDENTIALS │ Failed to set up unit's credentials. See │
│ │ │ ImportCredential=, LoadCredential= and │
│ │ │ SetCredential= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 245 │ EXIT_BPF │ Failed to apply BPF restrictions. See │
│ │ │ RestrictFileSystems= above. │
└───────────┴──────────────────────────────┴─────────────────────────────────────────────┘

Finally, the BSD operating systems define a set of exit codes, typically
defined on Linux systems too:

Table 10. BSD exit codes
┌───────────┬────────────────┬──────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼────────────────┼──────────────────────┤
│ 64 │ EX_USAGE │ Command line usage │
│ │ │ error │
├───────────┼────────────────┼──────────────────────┤
│ 65 │ EX_DATAERR │ Data format error │
├───────────┼────────────────┼──────────────────────┤
│ 66 │ EX_NOINPUT │ Cannot open input │
├───────────┼────────────────┼──────────────────────┤
│ 67 │ EX_NOUSER │ Addressee unknown │
├───────────┼────────────────┼──────────────────────┤
│ 68 │ EX_NOHOST │ Host name unknown │
├───────────┼────────────────┼──────────────────────┤
│ 69 │ EX_UNAVAILABLE │ Service unavailable │
├───────────┼────────────────┼──────────────────────┤
│ 70 │ EX_SOFTWARE │ internal software │
│ │ │ error │
├───────────┼────────────────┼──────────────────────┤
│ 71 │ EX_OSERR │ System error (e.g., │
│ │ │ cannot fork) │
├───────────┼────────────────┼──────────────────────┤
│ 72 │ EX_OSFILE │ Critical OS file │
│ │ │ missing │
├───────────┼────────────────┼──────────────────────┤
│ 73 │ EX_CANTCREAT │ Cannot create (user) │
│ │ │ output file │
├───────────┼────────────────┼──────────────────────┤
│ 74 │ EX_IOERR │ Input/output error │
├───────────┼────────────────┼──────────────────────┤
│ 75 │ EX_TEMPFAIL │ Temporary failure; │
│ │ │ user is invited to │
│ │ │ retry │
├───────────┼────────────────┼──────────────────────┤
│ 76 │ EX_PROTOCOL │ Remote error in │
│ │ │ protocol │
├───────────┼────────────────┼──────────────────────┤
│ 77 │ EX_NOPERM │ Permission denied │
├───────────┼────────────────┼──────────────────────┤
│ 78 │ EX_CONFIG │ Configuration error │
└───────────┴────────────────┴──────────────────────┘

EXAMPLES
Example 3. $MONITOR_* usage

A service myfailer.service which can trigger an OnFailure= dependency.

[Unit]
Description=Service which can trigger an OnFailure= dependency
OnFailure=myhandler.service

[Service]
ExecStart=/bin/myprogram

A service mysuccess.service which can trigger an OnSuccess= dependency.

[Unit]
Description=Service which can trigger an OnSuccess= dependency
OnSuccess=myhandler.service

[Service]
ExecStart=/bin/mysecondprogram

A service myhandler.service which can be triggered by any of the above
services.

[Unit]
Description=Acts on service failing or succeeding

[Service]
ExecStart=/bin/bash -c "echo $MONITOR_SERVICE_RESULT $MONITOR_EXIT_CODE $MONITOR_EXIT_STATUS $MONITOR_INVOCATION_ID $MONITOR_UNIT"

If myfailer.service were to run and exit in failure, then
myhandler.service would be triggered and the monitor variables would be
set as follows:

MONITOR_SERVICE_RESULT=exit-code
MONITOR_EXIT_CODE=exited
MONITOR_EXIT_STATUS=1
MONITOR_INVOCATION_ID=cc8fdc149b2b4ca698d4f259f4054236
MONITOR_UNIT=myfailer.service

If mysuccess.service were to run and exit in success, then
myhandler.service would be triggered and the monitor variables would be
set as follows:

MONITOR_SERVICE_RESULT=success
MONITOR_EXIT_CODE=exited
MONITOR_EXIT_STATUS=0
MONITOR_INVOCATION_ID=6ab9af147b8c4a3ebe36e7a5f8611697
MONITOR_UNIT=mysuccess.service

SEE ALSO
systemd(1), systemctl(1), systemd-analyze(1), journalctl(1), systemd-
system.conf(5), systemd.unit(5), systemd.service(5), systemd.socket(5),
systemd.swap(5), systemd.mount(5), systemd.kill(5), systemd.resource-
control(5), systemd.time(7), systemd.directives(7), tmpfiles.d(5),
exec(3), fork(2)

NOTES
1. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification

2. The /proc Filesystem
https://docs.kernel.org/filesystems/proc.html#mount-options

3. User/Group Name Syntax
https://systemd.io/USER_NAMES

4. No New Privileges Flag
https://docs.kernel.org/userspace-api/no_new_privs.html

5. JSON User Record
https://systemd.io/USER_RECORD

6. The /proc Filesystem
https://docs.kernel.org/filesystems/proc.html

7. id-mapped mounts
https://lwn.net/Articles/896255/

8. Kernel Samepage Merging
https://docs.kernel.org/admin-guide/mm/ksm.html

9. unicode scalar values
https://www.unicode.org/glossary/#unicode_scalar_value

10. unicode noncharacters
https://www.unicode.org/glossary/#noncharacter

11. unicode byte order mark
https://www.unicode.org/glossary/#byte_order_mark

12. POSIX shell unquoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_01

13. POSIX shell single-quoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_02

14. POSIX shell double-quoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_03

15. Base64
https://tools.ietf.org/html/rfc2045#section-6.8

16. Container Interface
https://systemd.io/CONTAINER_INTERFACE

17. DMI/SMBIOS
https://www.dmtf.org/standards/smbios

18. qemu
https://www.qemu.org/docs/master/system/index.html

19. System and Service Credentials
https://systemd.io/CREDENTIALS

20. Memory Pressure Handling
https://systemd.io/MEMORY_PRESSURE

21. LSB specification
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html

systemd 257.9 SYSTEMD.EXEC(5)

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