1SYSTEMD.JOURNAL-FIELDS(7)   systemd.journal-fields   SYSTEMD.JOURNAL-FIELDS(7)
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NAME

6       systemd.journal-fields - Special journal fields
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DESCRIPTION

9       Entries in the journal (as written by systemd-journald.service(8))
10       resemble a UNIX process environment block in syntax but with field
11       values that may include binary data, and with non-unique field names
12       permitted. Primarily, field values are formatted UTF-8 text strings —
13       binary encoding is used only where formatting as UTF-8 text strings
14       makes little sense. New fields may freely be defined by applications,
15       but a few fields have special meanings, which are listed below.
16       Typically, fields may only appear once per log entry, however there are
17       special exceptions: some fields may appear more than once per entry, in
18       which case this is explicitly mentioned below. Even though the logging
19       subsystem makes no restrictions on which fields to accept non-unique
20       values for, it is strongly recommended to avoid relying on this for the
21       fields listed below (except where listed otherwise, as mentioned) in
22       order to avoid unnecessary incompatibilities with other applications.
23

USER JOURNAL FIELDS

25       User fields are fields that are directly passed from clients and stored
26       in the journal.
27
28       MESSAGE=
29           The human-readable message string for this entry. This is supposed
30           to be the primary text shown to the user. It is usually not
31           translated (but might be in some cases), and is not supposed to be
32           parsed for metadata. In order to encode multiple lines in a single
33           log entry, separate them by newline characters (ASCII code 10), but
34           encode them as a single MESSAGE= field. Do not add multiple values
35           of this field type to the same entry (also see above), as consuming
36           applications generally do not expect this and are unlikely to show
37           all values in that case.
38
39       MESSAGE_ID=
40           A 128-bit message identifier ID for recognizing certain message
41           types, if this is desirable. This should contain a 128-bit ID
42           formatted as a lower-case hexadecimal string, without any
43           separating dashes or suchlike. This is recommended to be a
44           UUID-compatible ID, but this is not enforced, and formatted
45           differently. Developers can generate a new ID for this purpose with
46           systemd-id128 new.
47
48       PRIORITY=
49           A priority value between 0 ("emerg") and 7 ("debug") formatted as a
50           decimal string. This field is compatible with syslog's priority
51           concept.
52
53       CODE_FILE=, CODE_LINE=, CODE_FUNC=
54           The code location generating this message, if known. Contains the
55           source filename, the line number and the function name.
56
57       ERRNO=
58           The low-level Unix error number causing this entry, if any.
59           Contains the numeric value of errno(3) formatted as a decimal
60           string.
61
62       INVOCATION_ID=, USER_INVOCATION_ID=
63           A randomized, unique 128-bit ID identifying each runtime cycle of
64           the unit. This is different from _SYSTEMD_INVOCATION_ID in that it
65           is only used for messages coming from systemd code (e.g. logs from
66           the system/user manager or from forked processes performing
67           systemd-related setup).
68
69       SYSLOG_FACILITY=, SYSLOG_IDENTIFIER=, SYSLOG_PID=, SYSLOG_TIMESTAMP=
70           Syslog compatibility fields containing the facility (formatted as
71           decimal string), the identifier string (i.e. "tag"), the client
72           PID, and the timestamp as specified in the original datagram. (Note
73           that the tag is usually derived from glibc's
74           program_invocation_short_name variable, see
75           program_invocation_short_name(3).)
76
77           Note that the journal service does not validate the values of any
78           structured journal fields whose name is not prefixed with an
79           underscore, and this includes any syslog related fields such as
80           these. Hence, applications that supply a facility, PID, or log
81           level are expected to do so properly formatted, i.e. as numeric
82           integers formatted as decimal strings.
83
84       SYSLOG_RAW=
85           The original contents of the syslog line as received in the syslog
86           datagram. This field is only included if the MESSAGE= field was
87           modified compared to the original payload or the timestamp could
88           not be located properly and is not included in SYSLOG_TIMESTAMP=.
89           Message truncation occurs when the message contains leading or
90           trailing whitespace (trailing and leading whitespace is stripped),
91           or it contains an embedded NUL byte (the NUL byte and anything
92           after it is not included). Thus, the original syslog line is either
93           stored as SYSLOG_RAW= or it can be recreated based on the stored
94           priority and facility, timestamp, identifier, and the message
95           payload in MESSAGE=.
96
97       DOCUMENTATION=
98           A documentation URL with further information about the topic of the
99           log message. Tools such as journalctl will include a hyperlink to
100           an URL specified this way in their output. Should be an "http://",
101           "https://", "file:/", "man:" or "info:" URL.
102
103       TID=
104           The numeric thread ID (TID) the log message originates from.
105
106       UNIT=, USER_UNIT=
107           The name of a unit. Used by the system and user managers when
108           logging about specific units.
109
110           When --unit=name or --user-unit=name are used with journalctl(1), a
111           match pattern that includes "UNIT=name.service" or
112           "USER_UNIT=name.service" will be generated.
113

TRUSTED JOURNAL FIELDS

115       Fields prefixed with an underscore are trusted fields, i.e. fields that
116       are implicitly added by the journal and cannot be altered by client
117       code.
118
119       _PID=, _UID=, _GID=
120           The process, user, and group ID of the process the journal entry
121           originates from formatted as a decimal string. Note that entries
122           obtained via "stdout" or "stderr" of forked processes will contain
123           credentials valid for a parent process (that initiated the
124           connection to systemd-journald).
125
126       _COMM=, _EXE=, _CMDLINE=
127           The name, the executable path, and the command line of the process
128           the journal entry originates from.
129
130       _CAP_EFFECTIVE=
131           The effective capabilities(7) of the process the journal entry
132           originates from.
133
134       _AUDIT_SESSION=, _AUDIT_LOGINUID=
135           The session and login UID of the process the journal entry
136           originates from, as maintained by the kernel audit subsystem.
137
138       _SYSTEMD_CGROUP=, _SYSTEMD_SLICE=, _SYSTEMD_UNIT=, _SYSTEMD_USER_UNIT=,
139       _SYSTEMD_USER_SLICE=, _SYSTEMD_SESSION=, _SYSTEMD_OWNER_UID=
140           The control group path in the systemd hierarchy, the systemd slice
141           unit name, the systemd unit name, the unit name in the systemd user
142           manager (if any), the systemd session ID (if any), and the owner
143           UID of the systemd user unit or systemd session (if any) of the
144           process the journal entry originates from.
145
146       _SELINUX_CONTEXT=
147           The SELinux security context (label) of the process the journal
148           entry originates from.
149
150       _SOURCE_REALTIME_TIMESTAMP=
151           The earliest trusted timestamp of the message, if any is known that
152           is different from the reception time of the journal. This is the
153           time in microseconds since the epoch UTC, formatted as a decimal
154           string.
155
156       _BOOT_ID=
157           The kernel boot ID for the boot the message was generated in,
158           formatted as a 128-bit hexadecimal string.
159
160       _MACHINE_ID=
161           The machine ID of the originating host, as available in machine-
162           id(5).
163
164       _SYSTEMD_INVOCATION_ID=
165           The invocation ID for the runtime cycle of the unit the message was
166           generated in, as available to processes of the unit in
167           $INVOCATION_ID (see systemd.exec(5)).
168
169       _HOSTNAME=
170           The name of the originating host.
171
172       _TRANSPORT=
173           How the entry was received by the journal service. Valid transports
174           are:
175
176           audit
177               for those read from the kernel audit subsystem
178
179           driver
180               for internally generated messages
181
182           syslog
183               for those received via the local syslog socket with the syslog
184               protocol
185
186           journal
187               for those received via the native journal protocol
188
189           stdout
190               for those read from a service's standard output or error output
191
192           kernel
193               for those read from the kernel
194
195       _STREAM_ID=
196           Only applies to "_TRANSPORT=stdout" records: specifies a randomized
197           128bit ID assigned to the stream connection when it was first
198           created. This ID is useful to reconstruct individual log streams
199           from the log records: all log records carrying the same stream ID
200           originate from the same stream.
201
202       _LINE_BREAK=
203           Only applies to "_TRANSPORT=stdout" records: indicates that the log
204           message in the standard output/error stream was not terminated with
205           a normal newline character ("\n", i.e. ASCII 10). Specifically,
206           when set this field is one of nul (in case the line was terminated
207           by a NUL byte), line-max (in case the maximum log line length was
208           reached, as configured with LineMax= in journald.conf(5)), eof (if
209           this was the last log record of a stream and the stream ended
210           without a final newline character), or pid-change (if the process
211           which generated the log output changed in the middle of a line).
212           Note that this record is not generated when a normal newline
213           character was used for marking the log line end.
214
215       _NAMESPACE=
216           If this file was written by a systemd-journald instance managing a
217           journal namespace that is not the default, this field contains the
218           namespace identifier. See systemd-journald.service(8) for details
219           about journal namespaces.
220
221       _RUNTIME_SCOPE=
222           A string field that specifies the runtime scope in which the
223           message was logged. If "initrd", the log message was processed
224           while the system was running inside the initrd. If "system", the
225           log message was generated after the system switched execution to
226           the host root filesystem.
227

KERNEL JOURNAL FIELDS

229       Kernel fields are fields that are used by messages originating in the
230       kernel and stored in the journal.
231
232       _KERNEL_DEVICE=
233           The kernel device name. If the entry is associated to a block
234           device, contains the major and minor numbers of the device node,
235           separated by ":" and prefixed by "b". Similarly for character
236           devices, but prefixed by "c". For network devices, this is the
237           interface index prefixed by "n". For all other devices, this is the
238           subsystem name prefixed by "+", followed by ":", followed by the
239           kernel device name.
240
241       _KERNEL_SUBSYSTEM=
242           The kernel subsystem name.
243
244       _UDEV_SYSNAME=
245           The kernel device name as it shows up in the device tree below
246           /sys/.
247
248       _UDEV_DEVNODE=
249           The device node path of this device in /dev/.
250
251       _UDEV_DEVLINK=
252           Additional symlink names pointing to the device node in /dev/. This
253           field is frequently set more than once per entry.
254

FIELDS TO LOG ON BEHALF OF A DIFFERENT PROGRAM

256       Fields in this section are used by programs to specify that they are
257       logging on behalf of another program or unit.
258
259       Fields used by the systemd-coredump coredump kernel helper:
260
261       COREDUMP_UNIT=, COREDUMP_USER_UNIT=
262           Used to annotate messages containing coredumps from system and
263           session units. See coredumpctl(1).
264
265       Privileged programs (currently UID 0) may attach OBJECT_PID= to a
266       message. This will instruct systemd-journald to attach additional
267       fields on behalf of the caller:
268
269       OBJECT_PID=PID
270           PID of the program that this message pertains to.
271
272       OBJECT_UID=, OBJECT_GID=, OBJECT_COMM=, OBJECT_EXE=, OBJECT_CMDLINE=,
273       OBJECT_AUDIT_SESSION=, OBJECT_AUDIT_LOGINUID=, OBJECT_SYSTEMD_CGROUP=,
274       OBJECT_SYSTEMD_SESSION=, OBJECT_SYSTEMD_OWNER_UID=,
275       OBJECT_SYSTEMD_UNIT=, OBJECT_SYSTEMD_USER_UNIT=
276           These are additional fields added automatically by
277           systemd-journald. Their meaning is the same as _UID=, _GID=,
278           _COMM=, _EXE=, _CMDLINE=, _AUDIT_SESSION=, _AUDIT_LOGINUID=,
279           _SYSTEMD_CGROUP=, _SYSTEMD_SESSION=, _SYSTEMD_UNIT=,
280           _SYSTEMD_USER_UNIT=, and _SYSTEMD_OWNER_UID= as described above,
281           except that the process identified by PID is described, instead of
282           the process which logged the message.
283

ADDRESS FIELDS

285       During serialization into external formats, such as the Journal Export
286       Format[1] or the Journal JSON Format[2], the addresses of journal
287       entries are serialized into fields prefixed with double underscores.
288       Note that these are not proper fields when stored in the journal but
289       for addressing metadata of entries. They cannot be written as part of
290       structured log entries via calls such as sd_journal_send(3). They may
291       also not be used as matches for sd_journal_add_match(3).
292
293       __CURSOR=
294           The cursor for the entry. A cursor is an opaque text string that
295           uniquely describes the position of an entry in the journal and is
296           portable across machines, platforms and journal files.
297
298       __REALTIME_TIMESTAMP=
299           The wallclock time (CLOCK_REALTIME) at the point in time the entry
300           was received by the journal, in microseconds since the epoch UTC,
301           formatted as a decimal string. This has different properties from
302           "_SOURCE_REALTIME_TIMESTAMP=", as it is usually a bit later but
303           more likely to be monotonic.
304
305       __MONOTONIC_TIMESTAMP=
306           The monotonic time (CLOCK_MONOTONIC) at the point in time the entry
307           was received by the journal in microseconds, formatted as a decimal
308           string. To be useful as an address for the entry, this should be
309           combined with the boot ID in "_BOOT_ID=".
310

SEE ALSO

312       systemd(1), systemd-journald.service(8), journalctl(1),
313       journald.conf(5), sd-journal(3), coredumpctl(1), systemd.directives(7)
314

NOTES

316        1. Journal Export Format
317           https://systemd.io/JOURNAL_EXPORT_FORMATS#journal-export-format
318
319        2. Journal JSON Format
320           https://systemd.io/JOURNAL_EXPORT_FORMATS#journal-json-format
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324systemd 253                                          SYSTEMD.JOURNAL-FIELDS(7)
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