PAM_SYSTEMD(8) pam_systemd PAM_SYSTEMD(8)
NAME
pam_systemd - Register user sessions in the systemd login manager
SYNOPSIS
pam_systemd.so
DESCRIPTION
pam_systemd registers user sessions with the systemd login manager
systemd-logind.service(8), and hence the systemd control group
hierarchy.
The module also applies various resource management and runtime
parameters to the new session, as configured in the JSON User Records[1]
of the user, when one is defined.
On login, this module — in conjunction with systemd-logind.service —
ensures the following:
1. If it does not exist yet, the user runtime directory /run/user/$UID
is either created or mounted as new "tmpfs" file system with quota
applied, and its ownership changed to the user that is logging in.
2. The $XDG_SESSION_ID environment variable is initialized. If auditing
is available and pam_loginuid.so was run before this module (which
is highly recommended), the variable is initialized from the
auditing session id (/proc/self/sessionid). Otherwise, an
independent session counter is used.
3. A new systemd scope unit is created for the session. If this is the
first concurrent session of the user, an implicit per-user slice
unit below user.slice is automatically created and the scope placed
into it. An instance of the system service user@.service, which runs
the systemd user manager instance, is started.
4. The "$TZ", "$EMAIL" and "$LANG" environment variables are configured
for the user, based on the respective data from the user's JSON
record (if it is defined). Moreover, any environment variables
explicitly configured in the user record are imported, and the
umask, nice level, and resource limits initialized.
On logout, this module ensures the following:
1. If enabled in logind.conf(5) (KillUserProcesses=), all processes of
the session are terminated. If the last concurrent session of a user
ends, the user's systemd instance will be terminated too, and so
will the user's slice unit.
2. If the last concurrent session of a user ends, the user runtime
directory /run/user/$UID and all its contents are removed, too.
If the system was not booted up with systemd as init system, this module
does nothing and immediately returns PAM_SUCCESS.
OPTIONS
The following options are understood:
class=
Takes a string argument which sets the session class. The
XDG_SESSION_CLASS environment variable (see below) takes precedence.
See sd_session_get_class(3) for a way to query the class of a
session. The following session classes are defined:
Table 1. Session Classes
┌──────────────────┬────────────────────────────┐
│ Name │ Explanation │
├──────────────────┼────────────────────────────┤
│ user │ A regular interactive user │
│ │ session. This is the │
│ │ default class for sessions │
│ │ for which a TTY or X │
│ │ display is known at │
│ │ session registration time. │
├──────────────────┼────────────────────────────┤
│ user-early │ Similar to user but │
│ │ sessions of this class are │
│ │ not ordered after systemd- │
│ │ user-sessions.service(8), │
│ │ i.e. may be started before │
│ │ regular sessions are │
│ │ allowed to be established. │
│ │ This session class is the │
│ │ default for sessions of │
│ │ the root user that would │
│ │ otherwise qualify for the │
│ │ user class, see above. │
│ │ (Added in v256.) │
├──────────────────┼────────────────────────────┤
│ user-incomplete │ Similar to user but for │
│ │ sessions which are not │
│ │ fully set up yet, i.e. │
│ │ have no home directory │
│ │ mounted or similar. This │
│ │ is used by systemd- │
│ │ homed.service(8) to allow │
│ │ users to log in via ssh(1) │
│ │ before their home │
│ │ directory is mounted, │
│ │ delaying the mount until │
│ │ the user provided the │
│ │ unlock password. Sessions │
│ │ of this class are upgraded │
│ │ to the regular user class │
│ │ once the home directory is │
│ │ activated. │
├──────────────────┼────────────────────────────┤
│ greeter │ Similar to user but for │
│ │ sessions that are spawned │
│ │ by a display manager │
│ │ ephemerally and which │
│ │ prompt the user for login │
│ │ credentials. │
├──────────────────┼────────────────────────────┤
│ lock-screen │ Similar to user but for │
│ │ sessions that are spawned │
│ │ by a display manager │
│ │ ephemerally and which show │
│ │ a lock screen that can be │
│ │ used to unlock locked user │
│ │ accounts or sessions. │
├──────────────────┼────────────────────────────┤
│ background │ Used for background │
│ │ sessions, such as those │
│ │ invoked by cron(8) and │
│ │ similar tools. This is the │
│ │ default class for sessions │
│ │ for which no TTY or X │
│ │ display is known at │
│ │ session registration time. │
├──────────────────┼────────────────────────────┤
│ background-light │ Similar to background, but │
│ │ sessions of this class │
│ │ will not pull in the │
│ │ user@.service(5) of the │
│ │ user, and thus possibly │
│ │ have no services of the │
│ │ user running. (Added in │
│ │ v256.) │
├──────────────────┼────────────────────────────┤
│ manager │ The user@.service(5) │
│ │ service of the user is │
│ │ registered under this │
│ │ session class. (Added in │
│ │ v256.) │
├──────────────────┼────────────────────────────┤
│ manager-early │ Similar to manager, but │
│ │ for the root user. Compare │
│ │ with the user vs. │
│ │ user-early situation. │
│ │ (Added in v256.) │
└──────────────────┴────────────────────────────┘
Added in version 197.
type=
Takes a string argument which sets the session type. The
XDG_SESSION_TYPE environment variable (see below) takes precedence.
One of unspecified, tty, x11, wayland, mir, or web. See
sd_session_get_type(3) for details about the session type.
Added in version 209.
desktop=
Takes a single, short identifier string for the desktop environment.
The XDG_SESSION_DESKTOP environment variable (see below) takes
precedence. This may be used to indicate the session desktop used,
where this applies and if this information is available. For
example: GNOME, or KDE. It is recommended to use the same
identifiers and capitalization as for $XDG_CURRENT_DESKTOP, as
defined by the Desktop Entry Specification[2]. (However, note that
the option only takes a single item, and not a colon-separated list
like $XDG_CURRENT_DESKTOP.) See sd_session_get_desktop(3) for
further details.
Added in version 240.
default-capability-bounding-set=, default-capability-ambient-set=
Takes a comma-separated list of process capabilities (e.g.
CAP_WAKE_ALARM, CAP_BLOCK_SUSPEND, ...) to set for the invoked
session's processes, if the user record does not encode appropriate
sets of capabilities directly. See capabilities(7) for details on
the capabilities concept. If not specified, the default bounding set
is left as is (i.e. usually contains the full set of capabilities).
The default ambient set is set to CAP_WAKE_ALARM for regular users
if the PAM session is associated with a local seat or if it is
invoked for the systemd user service user@.service. Otherwise,
defaults to the empty set.
Added in version 254.
debug[=]
Takes an optional boolean argument. If yes or without the argument,
the module will log debugging information as it operates.
MODULE TYPES PROVIDED
Only session is provided.
ENVIRONMENT
The following environment variables are initialized by the module and
available to the processes of the user's session:
$XDG_SESSION_ID
A short session identifier, suitable to be used in filenames. The
string itself should be considered opaque, although often it is just
the audit session ID as reported by /proc/self/sessionid. Each ID
will be assigned only once during machine uptime. It may hence be
used to uniquely label files or other resources of this session.
Combine this ID with the boot identifier, as returned by
sd_id128_get_boot(3), for a globally unique identifier.
$XDG_RUNTIME_DIR
Path to a user-private user-writable directory that is bound to the
user login time on the machine. It is automatically created the
first time a user logs in and removed on the user's final logout. If
a user logs in twice at the same time, both sessions will see the
same $XDG_RUNTIME_DIR and the same contents. If a user logs in once,
then logs out again, and logs in again, the directory contents will
have been lost in between, but applications should not rely on this
behavior and must be able to deal with stale files. To store
session-private data in this directory, the user should include the
value of $XDG_SESSION_ID in the filename. This directory shall be
used for runtime file system objects such as AF_UNIX sockets, FIFOs,
PID files and similar. It is guaranteed that this directory is local
and offers the greatest possible file system feature set the
operating system provides. For further details, see the XDG Base
Directory Specification[3]. $XDG_RUNTIME_DIR is not set if the
current user is not the original user of the session.
$TZ, $EMAIL, $LANG
If a JSON user record is known for the user logging in these
variables are initialized from the respective data in the record.
Added in version 245.
$SHELL_PROMPT_PREFIX, $SHELL_PROMPT_SUFFIX, $SHELL_WELCOME
These environment variables are initialized from the service
credentials "shell.prompt.prefix", "shell.prompt.suffix" and
"shell.welcome" if set. They are passed to the invoked session
processes, where they are imported into any shell prompt
(specifically $SHELL_PROMPT_PREFIX is added as prefix to $PS1, and
$SHELL_PROMPT_SUFFIX as suffix) or printed on screen when a shell
first initializes.
Added in version 257.
The following environment variables are read by the module and may be
used by the PAM service to pass metadata to the module. If these
variables are not set when the PAM module is invoked but can be
determined otherwise they are set by the module, so that these variables
are initialized for the session and applications if known at all.
$XDG_SESSION_TYPE
The session type. This may be used instead of type= on the module
parameter line, and is usually preferred.
Added in version 209.
$XDG_SESSION_CLASS
The session class. This may be used instead of class= on the module
parameter line, and is usually preferred.
Added in version 209.
$XDG_SESSION_DESKTOP
The desktop identifier. This may be used instead of desktop= on the
module parameter line, and is usually preferred.
Added in version 209.
$XDG_SEAT
The seat name the session shall be registered for, if any.
Added in version 209.
$XDG_VTNR
The VT number the session shall be registered for, if any. (Only
applies to seats with a VT available, such as "seat0")
Added in version 209.
If not set, pam_systemd will initialize $XDG_SEAT and $XDG_VTNR based on
the $DISPLAY variable (if the latter is set).
SESSION LIMITS
PAM modules earlier in the stack, that is those that come before
pam_systemd.so, can set session scope limits using the PAM context
objects. The data for these objects is provided as NUL-terminated C
strings and maps directly to the respective unit resource control
directives. Note that these limits apply to individual sessions of the
user, they do not apply to all user processes as a combined whole. In
particular, the per-user user@.service unit instance, which runs the
systemd --user manager process and its children, and is tracked outside
of any session, being shared by all the user's sessions, is not covered
by these limits.
See systemd.resource-control(5) for more information about the
resources. Also, see pam_set_data(3) for additional information about
how to set the context objects.
systemd.memory_max=
Sets unit MemoryMax=.
Added in version 239.
systemd.tasks_max=
Sets unit TasksMax=.
Added in version 239.
systemd.cpu_weight=
Sets unit CPUWeight=.
Added in version 239.
systemd.io_weight=
Sets unit IOWeight=.
Added in version 239.
systemd.runtime_max_sec=
Sets unit RuntimeMaxSec=.
Added in version 244.
Example data as can be provided from an another PAM module:
pam_set_data(handle, "systemd.memory_max", (void *)"200M", cleanup);
pam_set_data(handle, "systemd.tasks_max", (void *)"50", cleanup);
pam_set_data(handle, "systemd.cpu_weight", (void *)"100", cleanup);
pam_set_data(handle, "systemd.io_weight", (void *)"340", cleanup);
pam_set_data(handle, "systemd.runtime_max_sec", (void *)"3600", cleanup);
EXAMPLE
Here's an example PAM configuration fragment that allows users sessions
to be managed by systemd-logind.service:
#%PAM-1.0
auth sufficient pam_unix.so
-auth sufficient pam_systemd_home.so
auth required pam_deny.so
account required pam_nologin.so
-account sufficient pam_systemd_home.so
account sufficient pam_unix.so
account required pam_permit.so
-password sufficient pam_systemd_home.so
password sufficient pam_unix.so sha512 shadow try_first_pass
password required pam_deny.so
-session optional pam_keyinit.so revoke
-session optional pam_loginuid.so
-session optional pam_systemd_home.so
-session optional pam_systemd.so
session required pam_unix.so
SEE ALSO
systemd(1), systemd-user-sessions.service(8), user@.service(5), systemd-
logind.service(8), logind.conf(5), loginctl(1), pam_systemd_home(8),
pam.conf(5), pam.d(5), pam(8), pam_loginuid(8), systemd.scope(5),
systemd.slice(5), systemd.service(5)
NOTES
1. JSON User Records
https://systemd.io/USER_RECORD
2. Desktop Entry Specification
https://standards.freedesktop.org/desktop-entry-spec/latest/
3. XDG Base Directory Specification
https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
systemd 257.9 PAM_SYSTEMD(8)
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