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 entry.
USER JOURNAL FIELDS
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 meta data.
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
A priority value between 0 ("emerg") and 7 ("debug") formatted as a
decimal string. This field is compatible with syslog's priority
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_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
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
_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
The session and login UID of the process the journal entry
originates from, as maintained by the kernel audit subsystem.
_SYSTEMD_CGROUP=, _SYSTEMD_SESSION=, _SYSTEMD_UNIT=,
_SYSTEMD_USER_UNIT=, _SYSTEMD_OWNER_UID=, _SYSTEMD_SLICE=
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 of the process the journal entry
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
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 machine-
The name of the originating host.
How the entry was received by the journal service. Valid transports
for internally generated messages
for those received via the local syslog socket with the syslog
for those received via the native journal protocol
for those read from a service's standard output or error output
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 device name.
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 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:
Used to annotate messages containing coredumps from system and
session units. See systemd-coredumpctl(1).
Priviledged 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=, OBJECT_AUDIT_LOGINUID=, OBJECT_SYSTEMD_CGROUP=,
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.
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 with the boot ID in "_BOOT_ID=".
systemd(1), journalctl(1), journald.conf(5), sd-journal(3), systemd-
1. Journal Export Format
2. Journal JSON Format