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SYSTEMD.JOURNAL-FIELDS(7)   systemd.journal-fields   SYSTEMD.JOURNAL-FIELDS(7)
NAME
       systemd.journal-fields - Special journal fields
DESCRIPTION
       Entries in the journal resemble an environment block in their syntax
       but with fields that can include binary data. Primarily, fields are
       formatted UTF-8 text strings, and binary formatting 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
       meaning. All fields with special meanings are optional. In some cases,
       fields may appear more than once per entry.
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.
       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
           journalctl --new-id128.
       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.
       SYSLOG_FACILITY=, SYSLOG_IDENTIFIER=, SYSLOG_PID=
           Syslog compatibility fields containing the facility (formatted as
           decimal string), the identifier string (i.e. "tag"), and the client
           PID. (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.
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_SESSION=, _SYSTEMD_OWNER_UID=
           The control group path in the systemd hierarchy, the 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.
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, the major and minor of the device node, separated by ":"
           and prefixed by "b". Similar 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=".
SEE ALSO
       systemd(1), journalctl(1), journald.conf(5), sd-journal(3),
       coredumpctl(1), systemd.directives(7)
NOTES
        1. Journal Export Format
           https://www.freedesktop.org/wiki/Software/systemd/export
        2. Journal JSON Format
           https://www.freedesktop.org/wiki/Software/systemd/json
systemd 239                                          SYSTEMD.JOURNAL-FIELDS(7)