Ubuntu Manpage: systemd.journal-fields

Provided by: systemd_253.5-1ubuntu6.1_amd64

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.

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).

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 numeric integers formatted as
decimal strings.

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=.

DOCUMENTATION=
A documentation URL with further information about the topic of the log message. Tools
such as journalctl will include a hyperlink to an URL specified this way in their
output. Should be an "http://", "https://", "file:/", "man:" or "info:" URL.

TID=
The numeric thread ID (TID) the log message originates from.

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.

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, user, and group ID of the process the journal entry originates from
formatted as a decimal string. 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.

_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. This is the time in microseconds since the epoch
UTC, formatted as a decimal string.

_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 available 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)).

_HOSTNAME=
The name 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

driver
for internally generated messages

syslog
for those received via the local syslog socket with the syslog protocol

journal
for those received via the native journal protocol

stdout
for those read from a service's standard output or error output

kernel
for those read from the kernel

_STREAM_ID=
Only applies to "_TRANSPORT=stdout" records: specifies a randomized 128bit 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.

_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.

_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.

_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.

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.

       _KERNEL_SUBSYSTEM=
           The kernel subsystem name.

       _UDEV_SYSNAME=
           The kernel device name as it shows up in the device tree below /sys/.

       _UDEV_DEVNODE=
           The device node path of this device in /dev/.

       _UDEV_DEVLINK=
           Additional symlink names pointing to the device node in /dev/. This field is
           frequently set more than once per entry.

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).

       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.

       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.

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 string. 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 string. To be useful as an address
           for the entry, this should be combined with the boot ID in "_BOOT_ID=".

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