systemd.journal-fields - Special journal fields
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
USER JOURNAL FIELDS¶
User fields are fields that are directly passed from clients and stored in the
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
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-id.
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.
The low-level Unix error number causing this entry, if
any. Contains the numeric value of errno(3)
formatted as a decimal
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
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.
_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
systemd session ID (if any), the systemd unit name (if any), the systemd user
session unit name (if any), the owner UID of the systemd session (if any) and
the systemd slice unit 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 name of the originating host.
How the entry was received by the journal service. Valid
for those read from the kernel audit subsystem
for internally generated messages
for those received via the local syslog socket with the
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
KERNEL JOURNAL FIELDS¶
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
The kernel subsystem name.
The kernel device name as it shows up in the device tree
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 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
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.
OBJECT_UID=, OBJECT_GID=, OBJECT_COMM=,
OBJECT_EXE=, OBJECT_CMDLINE=, OBJECT_AUDIT_SESSION=,
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
During serialization into external formats, such as the Journal Export
Format or the Journal JSON Format, 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)
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=".
- Journal Export Format
- Journal JSON Format