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=".
NOTES¶
- 1.
- Journal Export Format
- 2.
- Journal JSON Format