man > systemd.journal-fields(7)

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 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=.

           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, 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.

           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. 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)).

           Added in version 233.

       _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

               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.

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=".

       __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 255                                                                SYSTEMD.JOURNAL-FIELDS(7)