man/systemd.journal-fields.xml

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   9 <refentry id="systemd.journal-fields">
  10
  11   <refentryinfo>
  12     <title>systemd.journal-fields</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>systemd.journal-fields</refentrytitle>
  18     <manvolnum>7</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>systemd.journal-fields</refname>
  23     <refpurpose>Special journal fields</refpurpose>
  24   </refnamediv>
  25
  26   <refsect1>
  27     <title>Description</title>
  28
  29     <para>Entries in the journal resemble an environment block in
  30     their syntax but with fields that can include binary data.
  31     Primarily, fields are formatted UTF-8 text strings, and binary
  32     formatting is used only where formatting as UTF-8 text strings
  33     makes little sense. New fields may freely be defined by
  34     applications, but a few fields have special meaning. All fields
  35     with special meanings are optional. In some cases, fields may
  36     appear more than once per entry.</para>
  37   </refsect1>
  38
  39   <refsect1>
  40     <title>User Journal Fields</title>
  41
  42     <para>User fields are fields that are directly passed from clients
  43     and stored in the journal.</para>
  44
  45     <variablelist class='journal-directives'>
  46       <varlistentry>
  47         <term><varname>MESSAGE=</varname></term>
  48         <listitem>
  49           <para>The human-readable message string for this entry. This
  50           is supposed to be the primary text shown to the user. It is
  51           usually not translated (but might be in some cases), and is
  52           not supposed to be parsed for metadata.</para>
  53         </listitem>
  54       </varlistentry>
  55
  56       <varlistentry>
  57         <term><varname>MESSAGE_ID=</varname></term>
  58         <listitem>
  59           <para>A 128-bit message identifier ID for recognizing
  60           certain message types, if this is desirable. This should
  61           contain a 128-bit ID formatted as a lower-case hexadecimal
  62           string, without any separating dashes or suchlike. This is
  63           recommended to be a UUID-compatible ID, but this is not
  64           enforced, and formatted differently. Developers can generate
  65           a new ID for this purpose with <command>journalctl
  66           <option>--new-id128</option></command>.
  67           </para>
  68         </listitem>
  69       </varlistentry>
  70
  71       <varlistentry>
  72         <term><varname>PRIORITY=</varname></term>
  73         <listitem>
  74           <para>A priority value between 0 (<literal>emerg</literal>)
  75           and 7 (<literal>debug</literal>) formatted as a decimal
  76           string. This field is compatible with syslog's priority
  77           concept.</para>
  78         </listitem>
  79       </varlistentry>
  80
  81       <varlistentry>
  82         <term><varname>CODE_FILE=</varname></term>
  83         <term><varname>CODE_LINE=</varname></term>
  84         <term><varname>CODE_FUNC=</varname></term>
  85         <listitem>
  86           <para>The code location generating this message, if known.
  87           Contains the source filename, the line number and the
  88           function name.</para>
  89         </listitem>
  90       </varlistentry>
  91
  92       <varlistentry>
  93         <term><varname>ERRNO=</varname></term>
  94         <listitem>
  95           <para>The low-level Unix error number causing this entry, if
  96           any. Contains the numeric value of
  97           <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  98           formatted as a decimal string.</para>
  99         </listitem>
 100       </varlistentry>
 101
 102       <varlistentry>
 103         <term><varname>SYSLOG_FACILITY=</varname></term>
 104         <term><varname>SYSLOG_IDENTIFIER=</varname></term>
 105         <term><varname>SYSLOG_PID=</varname></term>
 106         <listitem>
 107           <para>Syslog compatibility fields containing the facility
 108           (formatted as decimal string), the identifier string (i.e.
 109           "tag"), and the client PID. (Note that the tag is usually
 110           derived from glibc's
 111           <varname>program_invocation_short_name</varname> variable,
 112           see
 113           <citerefentry project='die-net'><refentrytitle>program_invocation_short_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>.)</para>
 114         </listitem>
 115
 116       </varlistentry>
 117     </variablelist>
 118   </refsect1>
 119
 120   <refsect1>
 121     <title>Trusted Journal Fields</title>
 122
 123     <para>Fields prefixed with an underscore are trusted fields, i.e.
 124     fields that are implicitly added by the journal and cannot be
 125     altered by client code.</para>
 126
 127     <variablelist class='journal-directives'>
 128       <varlistentry>
 129         <term><varname>_PID=</varname></term>
 130         <term><varname>_UID=</varname></term>
 131         <term><varname>_GID=</varname></term>
 132         <listitem>
 133           <para>The process, user, and group ID of the process the
 134           journal entry originates from formatted as a decimal
 135           string. Note that entries obtained via <literal>stdout</literal> or
 136           <literal>stderr</literal> of forked processes will contain credentials valid for a parent
 137           process (that initiated the connection to <command>systemd-journald</command>).</para>
 138         </listitem>
 139       </varlistentry>
 140
 141       <varlistentry>
 142         <term><varname>_COMM=</varname></term>
 143         <term><varname>_EXE=</varname></term>
 144         <term><varname>_CMDLINE=</varname></term>
 145         <listitem>
 146           <para>The name, the executable path, and the command line of
 147           the process the journal entry originates from.</para>
 148         </listitem>
 149       </varlistentry>
 150
 151       <varlistentry>
 152         <term><varname>_CAP_EFFECTIVE=</varname></term>
 153         <listitem>
 154           <para>The effective
 155           <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 156           of the process the journal entry originates from.</para>
 157         </listitem>
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term><varname>_AUDIT_SESSION=</varname></term>
 162         <term><varname>_AUDIT_LOGINUID=</varname></term>
 163         <listitem>
 164           <para>The session and login UID of the process the journal
 165           entry originates from, as maintained by the kernel audit
 166           subsystem.</para>
 167         </listitem>
 168       </varlistentry>
 169
 170       <varlistentry>
 171         <term><varname>_SYSTEMD_CGROUP=</varname></term>
 172         <term><varname>_SYSTEMD_SLICE=</varname></term>
 173         <term><varname>_SYSTEMD_UNIT=</varname></term>
 174         <term><varname>_SYSTEMD_USER_UNIT=</varname></term>
 175         <term><varname>_SYSTEMD_SESSION=</varname></term>
 176         <term><varname>_SYSTEMD_OWNER_UID=</varname></term>
 177
 178         <listitem>
 179           <para>The control group path in the systemd hierarchy, the
 180           the systemd slice unit name, the systemd unit name, the
 181           unit name in the systemd user manager (if any), the systemd
 182           session ID (if any), and the owner UID of the systemd user
 183           unit or systemd session (if any) of the process the journal
 184           entry originates from.</para>
 185         </listitem>
 186       </varlistentry>
 187
 188       <varlistentry>
 189         <term><varname>_SELINUX_CONTEXT=</varname></term>
 190         <listitem>
 191           <para>The SELinux security context (label) of the process
 192           the journal entry originates from.</para>
 193         </listitem>
 194       </varlistentry>
 195
 196       <varlistentry>
 197         <term><varname>_SOURCE_REALTIME_TIMESTAMP=</varname></term>
 198         <listitem>
 199           <para>The earliest trusted timestamp of the message, if any
 200           is known that is different from the reception time of the
 201           journal. This is the time in microseconds since the epoch
 202           UTC, formatted as a decimal string.</para>
 203         </listitem>
 204       </varlistentry>
 205
 206       <varlistentry>
 207         <term><varname>_BOOT_ID=</varname></term>
 208         <listitem>
 209           <para>The kernel boot ID for the boot the message was
 210           generated in, formatted as a 128-bit hexadecimal
 211           string.</para>
 212         </listitem>
 213       </varlistentry>
 214
 215       <varlistentry>
 216         <term><varname>_MACHINE_ID=</varname></term>
 217         <listitem>
 218           <para>The machine ID of the originating host, as available
 219           in
 220           <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 221         </listitem>
 222       </varlistentry>
 223
 224       <varlistentry>
 225         <term><varname>_SYSTEMD_INVOCATION_ID=</varname></term>
 226         <listitem>
 227           <para>The invocation ID for the runtime cycle of the unit
 228           the message was generated in, as available to processes
 229           of the unit in <varname>$INVOCATION_ID</varname> (see
 230           <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para>
 231         </listitem>
 232       </varlistentry>
 233
 234       <varlistentry>
 235         <term><varname>_HOSTNAME=</varname></term>
 236         <listitem>
 237           <para>The name of the originating host.</para>
 238         </listitem>
 239       </varlistentry>
 240
 241       <varlistentry>
 242         <term><varname>_TRANSPORT=</varname></term>
 243         <listitem>
 244           <para>How the entry was received by the journal service.
 245           Valid transports are:
 246           </para>
 247           <variablelist>
 248             <varlistentry>
 249               <term>
 250                 <option>audit</option>
 251               </term>
 252               <listitem>
 253                 <para>for those read from the kernel audit subsystem
 254                 </para>
 255               </listitem>
 256             </varlistentry>
 257
 258             <varlistentry>
 259               <term>
 260                 <option>driver</option>
 261               </term>
 262               <listitem>
 263                 <para>for internally generated messages
 264                 </para>
 265               </listitem>
 266             </varlistentry>
 267
 268             <varlistentry>
 269               <term>
 270                 <option>syslog</option>
 271               </term>
 272               <listitem>
 273                 <para>for those received via the local syslog socket
 274                 with the syslog protocol
 275                 </para>
 276               </listitem>
 277             </varlistentry>
 278
 279             <varlistentry>
 280               <term>
 281                 <option>journal</option>
 282               </term>
 283               <listitem>
 284                 <para>for those received via the native journal
 285                 protocol
 286                 </para>
 287               </listitem>
 288             </varlistentry>
 289
 290             <varlistentry>
 291               <term>
 292                 <option>stdout</option>
 293               </term>
 294               <listitem>
 295                 <para>for those read from a service's standard output
 296                 or error output
 297                 </para>
 298               </listitem>
 299             </varlistentry>
 300
 301             <varlistentry>
 302               <term>
 303                 <option>kernel</option>
 304               </term>
 305               <listitem>
 306                 <para>for those read from the kernel
 307                 </para>
 308               </listitem>
 309             </varlistentry>
 310           </variablelist>
 311         </listitem>
 312       </varlistentry>
 313       <varlistentry>
 314         <term><varname>_STREAM_ID=</varname></term>
 315         <listitem>
 316           <para>Only applies to <literal>_TRANSPORT=stdout</literal> records: specifies a randomized 128bit ID assigned
 317           to the stream connection when it was first created. This ID is useful to reconstruct individual log streams
 318           from the log records: all log records carrying the same stream ID originate from the same stream.</para>
 319         </listitem>
 320       </varlistentry>
 321       <varlistentry>
 322         <term><varname>_LINE_BREAK=</varname></term>
 323         <listitem>
 324           <para>Only applies to <literal>_TRANSPORT=stdout</literal> records: indicates that the log message in the
 325           standard output/error stream was not terminated with a normal newline character (<literal>\n</literal>,
 326           i.e. ASCII 10). Specifically, when set this field is one of <option>nul</option> (in case the line was
 327           terminated by a NUL byte), <option>line-max</option> (in case the maximum log line length was reached, as
 328           configured with <varname>LineMax=</varname> in
 329           <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or
 330           <option>eof</option> (if this was the last log record of a stream and the stream ended without a final
 331           newline character). Note that this record is not generated when a normal newline character was used for
 332           marking the log line end.</para>
 333         </listitem>
 334       </varlistentry>
 335     </variablelist>
 336   </refsect1>
 337
 338   <refsect1>
 339     <title>Kernel Journal Fields</title>
 340
 341     <para>Kernel fields are fields that are used by messages
 342     originating in the kernel and stored in the journal.</para>
 343
 344     <variablelist class='journal-directives'>
 345       <varlistentry>
 346         <term><varname>_KERNEL_DEVICE=</varname></term>
 347         <listitem>
 348           <para>The kernel device name. If the entry is associated to
 349           a block device, the major and minor of the device node,
 350           separated by <literal>:</literal> and prefixed by
 351           <literal>b</literal>. Similar for character devices but
 352           prefixed by <literal>c</literal>. For network devices, this
 353           is the interface index prefixed by <literal>n</literal>. For
 354           all other devices, this is the subsystem name prefixed by
 355           <literal>+</literal>, followed by <literal>:</literal>,
 356           followed by the kernel device name.</para>
 357         </listitem>
 358       </varlistentry>
 359       <varlistentry>
 360         <term><varname>_KERNEL_SUBSYSTEM=</varname></term>
 361         <listitem>
 362           <para>The kernel subsystem name.</para>
 363         </listitem>
 364       </varlistentry>
 365       <varlistentry>
 366         <term><varname>_UDEV_SYSNAME=</varname></term>
 367         <listitem>
 368           <para>The kernel device name as it shows up in the device
 369           tree below <filename>/sys</filename>.</para>
 370         </listitem>
 371       </varlistentry>
 372       <varlistentry>
 373         <term><varname>_UDEV_DEVNODE=</varname></term>
 374         <listitem>
 375           <para>The device node path of this device in
 376           <filename>/dev</filename>.</para>
 377         </listitem>
 378       </varlistentry>
 379       <varlistentry>
 380         <term><varname>_UDEV_DEVLINK=</varname></term>
 381         <listitem>
 382           <para>Additional symlink names pointing to the device node
 383           in <filename>/dev</filename>. This field is frequently set
 384           more than once per entry.</para>
 385         </listitem>
 386       </varlistentry>
 387     </variablelist>
 388   </refsect1>
 389
 390   <refsect1>
 391     <title>Fields to log on behalf of a different program</title>
 392
 393     <para>Fields in this section are used by programs to specify that
 394     they are logging on behalf of another program or unit.
 395     </para>
 396
 397     <para>Fields used by the <command>systemd-coredump</command>
 398     coredump kernel helper:
 399     </para>
 400
 401     <variablelist class='journal-directives'>
 402       <varlistentry>
 403         <term><varname>COREDUMP_UNIT=</varname></term>
 404         <term><varname>COREDUMP_USER_UNIT=</varname></term>
 405         <listitem>
 406           <para>Used to annotate messages containing coredumps from
 407           system and session units. See
 408           <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
 409           </para>
 410         </listitem>
 411       </varlistentry>
 412     </variablelist>
 413
 414     <para>Privileged programs (currently UID 0) may attach
 415     <varname>OBJECT_PID=</varname> to a message. This will instruct
 416     <command>systemd-journald</command> to attach additional fields on
 417     behalf of the caller:</para>
 418
 419     <variablelist class='journal-directives'>
 420       <varlistentry>
 421         <term><varname>OBJECT_PID=<replaceable>PID</replaceable></varname></term>
 422         <listitem>
 423           <para>PID of the program that this message pertains to.
 424           </para>
 425         </listitem>
 426       </varlistentry>
 427
 428       <varlistentry>
 429         <term><varname>OBJECT_UID=</varname></term>
 430         <term><varname>OBJECT_GID=</varname></term>
 431         <term><varname>OBJECT_COMM=</varname></term>
 432         <term><varname>OBJECT_EXE=</varname></term>
 433         <term><varname>OBJECT_CMDLINE=</varname></term>
 434         <term><varname>OBJECT_AUDIT_SESSION=</varname></term>
 435         <term><varname>OBJECT_AUDIT_LOGINUID=</varname></term>
 436         <term><varname>OBJECT_SYSTEMD_CGROUP=</varname></term>
 437         <term><varname>OBJECT_SYSTEMD_SESSION=</varname></term>
 438         <term><varname>OBJECT_SYSTEMD_OWNER_UID=</varname></term>
 439         <term><varname>OBJECT_SYSTEMD_UNIT=</varname></term>
 440         <term><varname>OBJECT_SYSTEMD_USER_UNIT=</varname></term>
 441         <listitem>
 442           <para>These are additional fields added automatically by
 443           <command>systemd-journald</command>. Their meaning is the
 444           same as
 445           <varname>_UID=</varname>,
 446           <varname>_GID=</varname>,
 447           <varname>_COMM=</varname>,
 448           <varname>_EXE=</varname>,
 449           <varname>_CMDLINE=</varname>,
 450           <varname>_AUDIT_SESSION=</varname>,
 451           <varname>_AUDIT_LOGINUID=</varname>,
 452           <varname>_SYSTEMD_CGROUP=</varname>,
 453           <varname>_SYSTEMD_SESSION=</varname>,
 454           <varname>_SYSTEMD_UNIT=</varname>,
 455           <varname>_SYSTEMD_USER_UNIT=</varname>, and
 456           <varname>_SYSTEMD_OWNER_UID=</varname>
 457           as described above, except that the process identified by
 458           <replaceable>PID</replaceable> is described, instead of the
 459           process which logged the message.</para>
 460         </listitem>
 461       </varlistentry>
 462     </variablelist>
 463
 464   </refsect1>
 465
 466   <refsect1>
 467     <title>Address Fields</title>
 468
 469     <para>During serialization into external formats, such as the
 470     <ulink
 471     url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal
 472     Export Format</ulink> or the <ulink
 473     url="https://www.freedesktop.org/wiki/Software/systemd/json">Journal
 474     JSON Format</ulink>, the addresses of journal entries are
 475     serialized into fields prefixed with double underscores. Note that
 476     these are not proper fields when stored in the journal but for
 477     addressing metadata of entries. They cannot be written as part of
 478     structured log entries via calls such as
 479     <citerefentry><refentrytitle>sd_journal_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 480     They may also not be used as matches for
 481     <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry></para>
 482
 483     <variablelist class='journal-directives'>
 484       <varlistentry>
 485         <term><varname>__CURSOR=</varname></term>
 486         <listitem>
 487           <para>The cursor for the entry. A cursor is an opaque text
 488           string that uniquely describes the position of an entry in
 489           the journal and is portable across machines, platforms and
 490           journal files.
 491           </para>
 492         </listitem>
 493       </varlistentry>
 494
 495       <varlistentry>
 496         <term><varname>__REALTIME_TIMESTAMP=</varname></term>
 497         <listitem>
 498           <para>The wallclock time
 499           (<constant>CLOCK_REALTIME</constant>) at the point in time
 500           the entry was received by the journal, in microseconds since
 501           the epoch UTC, formatted as a decimal string. This has
 502           different properties from
 503           <literal>_SOURCE_REALTIME_TIMESTAMP=</literal>, as it is
 504           usually a bit later but more likely to be monotonic.
 505           </para>
 506         </listitem>
 507       </varlistentry>
 508
 509       <varlistentry>
 510         <term><varname>__MONOTONIC_TIMESTAMP=</varname></term>
 511         <listitem>
 512           <para>The monotonic time
 513           (<constant>CLOCK_MONOTONIC</constant>) at the point in time
 514           the entry was received by the journal in microseconds,
 515           formatted as a decimal string. To be useful as an address
 516           for the entry, this should be combined with the boot ID in
 517           <literal>_BOOT_ID=</literal>.
 518           </para>
 519         </listitem>
 520       </varlistentry>
 521     </variablelist>
 522   </refsect1>
 523
 524   <refsect1>
 525       <title>See Also</title>
 526       <para>
 527         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 528         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 529         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 530         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 531         <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 532         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 533       </para>
 534   </refsect1>
 535
 536 </refentry>