SYSTEMD.JOURNAL-FIELDS(7) systemd.journal-fields SYSTEMD.JOURNAL-FIELDS(7)
NAME
systemd.journal-fields - Special journal fields
DESCRIPTION
Entries in the journal (as written by systemd-journald.service(8))
resemble a UNIX process environment block in syntax but with field
values that may include binary data, and with non-unique field names
permitted. Primarily, field values are formatted UTF-8 text strings —
binary encoding is used only where formatting as UTF-8 text strings
makes little sense. New fields may freely be defined by applications,
but a few fields have special meanings, which are listed below.
Typically, fields may only appear once per log entry, however there are
special exceptions: some fields may appear more than once per entry, in
which case this is explicitly mentioned below. Even though the logging
subsystem makes no restrictions on which fields to accept non-unique
values for, it is strongly recommended to avoid relying on this for the
fields listed below (except where listed otherwise, as mentioned) in
order to avoid unnecessary incompatibilities with other applications.
USER JOURNAL FIELDS
User fields are fields that are directly passed from clients and stored
in the journal.
MESSAGE=
The human-readable message string for this entry. This is supposed
to be the primary text shown to the user. It is usually not
translated (but might be in some cases), and is not supposed to be
parsed for metadata. In order to encode multiple lines in a single
log entry, separate them by newline characters (ASCII code 10), but
encode them as a single MESSAGE= field. Do not add multiple values
of this field type to the same entry (also see above), as consuming
applications generally do not expect this and are unlikely to show
all values in that case.
MESSAGE_ID=
A 128-bit message identifier ID for recognizing certain message
types, if this is desirable. This should contain a 128-bit ID
formatted as a lower-case hexadecimal string, without any separating
dashes or suchlike. This is recommended to be a UUID-compatible ID,
but this is not enforced, and formatted differently. Developers can
generate a new ID for this purpose with systemd-id128 new.
PRIORITY=
A priority value between 0 ("emerg") and 7 ("debug") formatted as a
decimal string. This field is compatible with syslog's priority
concept.
CODE_FILE=, CODE_LINE=, CODE_FUNC=
The code location generating this message, if known. Contains the
source filename, the line number and the function name.
ERRNO=
The low-level Unix error number causing this entry, if any. Contains
the numeric value of errno(3) formatted as a decimal string.
Added in version 188.
INVOCATION_ID=, USER_INVOCATION_ID=
A randomized, unique 128-bit ID identifying each runtime cycle of
the unit. This is different from _SYSTEMD_INVOCATION_ID in that it
is only used for messages coming from systemd code (e.g. logs from
the system/user manager or from forked processes performing
systemd-related setup).
Added in version 245.
SYSLOG_FACILITY=, SYSLOG_IDENTIFIER=, SYSLOG_PID=, SYSLOG_TIMESTAMP=
Syslog compatibility fields containing the facility (formatted as
decimal string), the identifier string (i.e. "tag"), the client PID,
and the timestamp as specified in the original datagram. (Note that
the tag is usually derived from glibc's
program_invocation_short_name variable, see
program_invocation_short_name(3).)
Note that the journal service does not validate the values of any
structured journal fields whose name is not prefixed with an
underscore, and this includes any syslog related fields such as
these. Hence, applications that supply a facility, PID, or log level
are expected to do so properly formatted, i.e. as integers formatted
as decimals.
SYSLOG_RAW=
The original contents of the syslog line as received in the syslog
datagram. This field is only included if the MESSAGE= field was
modified compared to the original payload or the timestamp could not
be located properly and is not included in SYSLOG_TIMESTAMP=.
Message truncation occurs when the message contains leading or
trailing whitespace (trailing and leading whitespace is stripped),
or it contains an embedded NUL byte (the NUL byte and anything after
it is not included). Thus, the original syslog line is either stored
as SYSLOG_RAW= or it can be recreated based on the stored priority
and facility, timestamp, identifier, and the message payload in
MESSAGE=.
Added in version 240.
DOCUMENTATION=
A documentation URL with further information about the topic of the
log message. Tools such as journalctl will include a hyperlink to a
URL specified this way in their output. Should be an "http://",
"https://", "file:/", "man:" or "info:" URL.
Added in version 246.
TID=
The numeric thread ID (TID) the log message originates from.
Added in version 247.
UNIT=, USER_UNIT=
The name of a unit. Used by the system and user managers when
logging about specific units.
When --unit=name or --user-unit=name are used with journalctl(1), a
match pattern that includes "UNIT=name.service" or
"USER_UNIT=name.service" will be generated.
Added in version 251.
TRUSTED JOURNAL FIELDS
Fields prefixed with an underscore are trusted fields, i.e. fields that
are implicitly added by the journal and cannot be altered by client
code.
_PID=, _UID=, _GID=
The process number, user number, and group number of the process the
journal entry originates from formatted as decimals. Note that
entries obtained via "stdout" or "stderr" of forked processes will
contain credentials valid for a parent process (that initiated the
connection to systemd-journald).
_COMM=, _EXE=, _CMDLINE=
The name, the executable path, and the command line of the process
the journal entry originates from.
_CAP_EFFECTIVE=
The effective capabilities(7) of the process the journal entry
originates from.
Added in version 206.
_AUDIT_SESSION=, _AUDIT_LOGINUID=
The session and login UID of the process the journal entry
originates from, as maintained by the kernel audit subsystem.
_SYSTEMD_CGROUP=, _SYSTEMD_SLICE=, _SYSTEMD_UNIT=, _SYSTEMD_USER_UNIT=,
_SYSTEMD_USER_SLICE=, _SYSTEMD_SESSION=, _SYSTEMD_OWNER_UID=
The control group path in the systemd hierarchy, the systemd slice
unit name, the systemd unit name, the unit name in the systemd user
manager (if any), the systemd session ID (if any), and the owner UID
of the systemd user unit or systemd session (if any) of the process
the journal entry originates from.
_SELINUX_CONTEXT=
The SELinux security context (label) of the process the journal
entry originates from.
_SOURCE_REALTIME_TIMESTAMP=
The earliest trusted timestamp of the message, if any is known that
is different from the reception time of the journal. The timestamp
is the CLOCK_REALTIME time in microseconds, formatted as a decimal.
_SOURCE_BOOTTIME_TIMESTAMP=
The earliest trusted timestamp of the message in the CLOCK_BOOTTIME
time, in the same format as _SOURCE_REALTIME_TIMESTAMP=.
Added in version 257.
_BOOT_ID=
The kernel boot ID for the boot the message was generated in,
formatted as a 128-bit hexadecimal string.
_MACHINE_ID=
The machine ID of the originating host, as described in machine-
id(5).
_SYSTEMD_INVOCATION_ID=
The invocation ID for the runtime cycle of the unit the message was
generated in, as available to processes of the unit in
$INVOCATION_ID (see systemd.exec(5)).
Added in version 233.
_HOSTNAME=
The hostname of the originating host.
_TRANSPORT=
How the entry was received by the journal service. Valid transports
are:
audit
for those read from the kernel audit subsystem
Added in version 227.
driver
for internally generated messages
Added in version 205.
syslog
for those received via the local syslog socket with the syslog
protocol
Added in version 205.
journal
for those received via the native journal protocol
Added in version 205.
stdout
for those read from a service's standard output or error output
Added in version 205.
kernel
for those read from the kernel
Added in version 205.
_STREAM_ID=
Only applies to "_TRANSPORT=stdout" records: specifies a randomized
128-bit ID assigned to the stream connection when it was first
created. This ID is useful to reconstruct individual log streams
from the log records: all log records carrying the same stream ID
originate from the same stream.
Added in version 235.
_LINE_BREAK=
Only applies to "_TRANSPORT=stdout" records: indicates that the log
message in the standard output/error stream was not terminated with
a normal newline character ("\n", i.e. ASCII 10). Specifically, when
set this field is one of nul (in case the line was terminated by a
NUL byte), line-max (in case the maximum log line length was
reached, as configured with LineMax= in journald.conf(5)), eof (if
this was the last log record of a stream and the stream ended
without a final newline character), or pid-change (if the process
which generated the log output changed in the middle of a line).
Note that this record is not generated when a normal newline
character was used for marking the log line end.
Added in version 235.
_NAMESPACE=
If this file was written by a systemd-journald instance managing a
journal namespace that is not the default, this field contains the
namespace identifier. See systemd-journald.service(8) for details
about journal namespaces.
Added in version 245.
_RUNTIME_SCOPE=
A string field that specifies the runtime scope in which the message
was logged. If "initrd", the log message was processed while the
system was running inside the initrd. If "system", the log message
was generated after the system switched execution to the host root
filesystem.
Added in version 252.
KERNEL JOURNAL FIELDS
Kernel fields are fields that are used by messages originating in the
kernel and stored in the journal.
_KERNEL_DEVICE=
The kernel device name. If the entry is associated to a block
device, contains the major and minor numbers of the device node,
separated by ":" and prefixed by "b". Similarly for character
devices, but prefixed by "c". For network devices, this is the
interface index prefixed by "n". For all other devices, this is the
subsystem name prefixed by "+", followed by ":", followed by the
kernel device name.
Added in version 189.
_KERNEL_SUBSYSTEM=
The kernel subsystem name.
Added in version 189.
_UDEV_SYSNAME=
The kernel device name as it shows up in the device tree below
/sys/.
Added in version 189.
_UDEV_DEVNODE=
The device node path of this device in /dev/.
Added in version 189.
_UDEV_DEVLINK=
Additional symlink names pointing to the device node in /dev/. This
field is frequently set more than once per entry.
Added in version 189.
FIELDS TO LOG ON BEHALF OF A DIFFERENT PROGRAM
Fields in this section are used by programs to specify that they are
logging on behalf of another program or unit.
Fields used by the systemd-coredump coredump kernel helper:
COREDUMP_UNIT=, COREDUMP_USER_UNIT=
Used to annotate messages containing coredumps from system and
session units. See coredumpctl(1).
Added in version 198.
Privileged programs (currently UID 0) may attach OBJECT_PID= to a
message. This will instruct systemd-journald to attach additional fields
on behalf of the caller:
OBJECT_PID=PID
PID of the program that this message pertains to.
Added in version 205.
OBJECT_UID=, OBJECT_GID=, OBJECT_COMM=, OBJECT_EXE=, OBJECT_CMDLINE=,
OBJECT_AUDIT_SESSION=, OBJECT_AUDIT_LOGINUID=, OBJECT_SYSTEMD_CGROUP=,
OBJECT_SYSTEMD_SESSION=, OBJECT_SYSTEMD_OWNER_UID=,
OBJECT_SYSTEMD_UNIT=, OBJECT_SYSTEMD_USER_UNIT=
These are additional fields added automatically by systemd-journald.
Their meaning is the same as _UID=, _GID=, _COMM=, _EXE=, _CMDLINE=,
_AUDIT_SESSION=, _AUDIT_LOGINUID=, _SYSTEMD_CGROUP=,
_SYSTEMD_SESSION=, _SYSTEMD_UNIT=, _SYSTEMD_USER_UNIT=, and
_SYSTEMD_OWNER_UID= as described above, except that the process
identified by PID is described, instead of the process which logged
the message.
Added in version 205.
OBJECT_SYSTEMD_INVOCATION_ID=
An additional field added automatically by systemd-journald. The
meaning is mostly the same as _SYSTEMD_INVOCATION_ID=, with the
difference described above.
Added in version 235.
ADDRESS FIELDS
During serialization into external formats, such as the Journal Export
Format[1] or the Journal JSON Format[2], the addresses of journal
entries are serialized into fields prefixed with double underscores.
Note that these are not proper fields when stored in the journal but for
addressing metadata of entries. They cannot be written as part of
structured log entries via calls such as sd_journal_send(3). They may
also not be used as matches for sd_journal_add_match(3).
__CURSOR=
The cursor for the entry. A cursor is an opaque text string that
uniquely describes the position of an entry in the journal and is
portable across machines, platforms and journal files.
__REALTIME_TIMESTAMP=
The wallclock time (CLOCK_REALTIME) at the point in time the entry
was received by the journal, in microseconds since the epoch UTC,
formatted as a decimal. This has different properties from
"_SOURCE_REALTIME_TIMESTAMP=", as it is usually a bit later but more
likely to be monotonic.
__MONOTONIC_TIMESTAMP=
The monotonic time (CLOCK_MONOTONIC) at the point in time the entry
was received by the journal in microseconds, formatted as a decimal.
To be useful as an address for the entry, this should be combined
with the boot ID in "_BOOT_ID=".
__SEQNUM=, __SEQNUM_ID=
The sequence number (and associated sequence number ID) of this
journal entry in the journal file it originates from. See
sd_journal_get_seqnum(3) for details.
Added in version 254.
SEE ALSO
systemd(1), systemd-journald.service(8), journalctl(1),
journald.conf(5), sd-journal(3), coredumpctl(1), systemd.directives(7)
NOTES
1. Journal Export Format
https://systemd.io/JOURNAL_EXPORT_FORMATS#journal-export-format
2. Journal JSON Format
https://systemd.io/JOURNAL_EXPORT_FORMATS#journal-json-format
systemd 257.9 SYSTEMD.JOURNAL-FIELDS(7)
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