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 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 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
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 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=.
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 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)) or eof
(if this was the last log record of a stream and the stream ended
without a final newline character). 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.
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), systemd-journald.service(8), 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 245 SYSTEMD.JOURNAL-FIELDS(7)