systemd.journal-fields(7) — Linux manual page



NAME         top

       systemd.journal-fields - Special journal fields

DESCRIPTION         top

       Entries in the journal (as written by systemd-journald.service(8))
       resemble a UNIX process environment block in syntax but with fields
       that may include binary data. Primarily, fields are formatted UTF-8
       text strings, and 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. All
       fields with special meanings are optional. In some cases, fields may
       appear more than once per entry.


       User fields are fields that are directly passed from clients and
       stored in the journal.

           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.

           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.

           A priority value between 0 ("emerg") and 7 ("debug") formatted as
           a decimal string. This field is compatible with syslog's priority

           The code location generating this message, if known. Contains the
           source filename, the line number and the function name.

           The low-level Unix error number causing this entry, if any.
           Contains the numeric value of errno(3) formatted as a decimal

           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 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

           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.

           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 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=.

           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
           a "http://", "https://", "file:/", "man:" or "info:" URL.


       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.

           The effective capabilities(7) of the process the journal entry
           originates from.

           The session and login UID of the process the journal entry
           originates from, as maintained by the kernel audit subsystem.

           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.

           The SELinux security context (label) of the process the journal
           entry originates from.

           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.

           The kernel boot ID for the boot the message was generated in,
           formatted as a 128-bit hexadecimal string.

           The machine ID of the originating host, as available in

           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)).

           The name of the originating host.

           How the entry was received by the journal service. Valid
           transports are:

               for those read from the kernel audit subsystem

               for internally generated messages

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

               for those received via the native journal protocol

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

               for those read from the kernel

           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.

           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.

           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.


       Kernel fields are fields that are used by messages originating in the
       kernel and stored in the journal.

           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

           The kernel subsystem name.

           The kernel device name as it shows up in the device tree below

           The device node path of this device in /dev.

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


       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:

           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:

           PID of the program that this message pertains to.

           These are additional fields added automatically by
           systemd-journald. Their meaning is the same as _UID=, _GID=,
           _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         top

       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

           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.

           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.

           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         top

       systemd(1), systemd-journald.service(8), journalctl(1),
       journald.conf(5), sd-journal(3), coredumpctl(1),

NOTES         top

        1. Journal Export Format

        2. Journal JSON Format

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-11.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

systemd 246                                        SYSTEMD.JOURNAL-FIELDS(7)

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