{
    "mode": "man",
    "parameter": "systemd.journal-fields",
    "section": "7",
    "url": "https://www.chedong.com/phpMan.php/man/systemd.journal-fields/7/json",
    "generated": "2026-11-09T19:15:52Z",
    "sections": {
        "NAME": {
            "content": "systemd.journal-fields - Special journal fields\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "Entries in the journal (as written by systemd-journald.service(8)) resemble a UNIX process\nenvironment block in syntax but with field values that may include binary data, and with\nnon-unique field names permitted. Primarily, field values are formatted UTF-8 text strings —\nbinary encoding is used only where formatting as UTF-8 text strings makes little sense. New\nfields may freely be defined by applications, but a few fields have special meanings, which\nare listed below. Typically, fields may only appear once per log entry, however there are\nspecial exceptions: some fields may appear more than once per entry, in which case this is\nexplicitly mentioned below. Even though the logging subsystem makes no restrictions on which\nfields to accept non-unique values for, it is strongly recommended to avoid relying on this\nfor the fields listed below (except where listed otherwise, as mentioned) in order to avoid\nunnecessary incompatibilities with other applications.\n",
            "subsections": []
        },
        "USER JOURNAL FIELDS": {
            "content": "User fields are fields that are directly passed from clients and stored in the journal.\n\nMESSAGE=\nThe human-readable message string for this entry. This is supposed to be the primary text\nshown to the user. It is usually not translated (but might be in some cases), and is not\nsupposed to be parsed for metadata. In order to encode multiple lines in a single log\nentry, separate them by newline characters (ASCII code 10), but encode them as a single\nMESSAGE= field. Do not add multiple values of this field type to the same entry (also see\nabove), as consuming applications generally do not expect this and are unlikely to show\nall values in that case.\n\nMESSAGEID=\nA 128-bit message identifier ID for recognizing certain message types, if this is\ndesirable. This should contain a 128-bit ID formatted as a lower-case hexadecimal string,\nwithout any separating dashes or suchlike. This is recommended to be a UUID-compatible\nID, but this is not enforced, and formatted differently. Developers can generate a new ID\nfor this purpose with systemd-id128 new.\n\nPRIORITY=\nA priority value between 0 (\"emerg\") and 7 (\"debug\") formatted as a decimal string. This\nfield is compatible with syslog's priority concept.\n\nCODEFILE=, CODELINE=, CODEFUNC=\nThe code location generating this message, if known. Contains the source filename, the\nline number and the function name.\n\nERRNO=\nThe low-level Unix error number causing this entry, if any. Contains the numeric value of\nerrno(3) formatted as a decimal string.\n\nAdded in version 188.\n\nINVOCATIONID=, USERINVOCATIONID=\nA randomized, unique 128-bit ID identifying each runtime cycle of the unit. This is\ndifferent from SYSTEMDINVOCATIONID in that it is only used for messages coming from\nsystemd code (e.g. logs from the system/user manager or from forked processes performing\nsystemd-related setup).\n\nAdded in version 245.\n\nSYSLOGFACILITY=, SYSLOGIDENTIFIER=, SYSLOGPID=, SYSLOGTIMESTAMP=\nSyslog compatibility fields containing the facility (formatted as decimal string), the\nidentifier string (i.e. \"tag\"), the client PID, and the timestamp as specified in the\noriginal datagram. (Note that the tag is usually derived from glibc's\nprograminvocationshortname variable, see programinvocationshortname(3).)\n\nNote that the journal service does not validate the values of any structured journal\nfields whose name is not prefixed with an underscore, and this includes any syslog\nrelated fields such as these. Hence, applications that supply a facility, PID, or log\nlevel are expected to do so properly formatted, i.e. as numeric integers formatted as\ndecimal strings.\n\nSYSLOGRAW=\nThe original contents of the syslog line as received in the syslog datagram. This field\nis only included if the MESSAGE= field was modified compared to the original payload or\nthe timestamp could not be located properly and is not included in SYSLOGTIMESTAMP=.\nMessage truncation occurs when the message contains leading or trailing whitespace\n(trailing and leading whitespace is stripped), or it contains an embedded NUL byte (the\nNUL byte and anything after it is not included). Thus, the original syslog line is either\nstored as SYSLOGRAW= or it can be recreated based on the stored priority and facility,\ntimestamp, identifier, and the message payload in MESSAGE=.\n\nAdded in version 240.\n\nDOCUMENTATION=\nA documentation URL with further information about the topic of the log message. Tools\nsuch as journalctl will include a hyperlink to a URL specified this way in their output.\nShould be an \"http://\", \"https://\", \"file:/\", \"man:\" or \"info:\" URL.\n\nAdded in version 246.\n\nTID=\nThe numeric thread ID (TID) the log message originates from.\n\nAdded in version 247.\n\nUNIT=, USERUNIT=\nThe name of a unit. Used by the system and user managers when logging about specific\nunits.\n\nWhen --unit=name or --user-unit=name are used with journalctl(1), a match pattern that\nincludes \"UNIT=name.service\" or \"USERUNIT=name.service\" will be generated.\n\nAdded in version 251.\n",
            "subsections": []
        },
        "TRUSTED JOURNAL FIELDS": {
            "content": "Fields prefixed with an underscore are trusted fields, i.e. fields that are implicitly added\nby the journal and cannot be altered by client code.\n\nPID=, UID=, GID=\nThe process, user, and group ID of the process the journal entry originates from\nformatted as a decimal string. Note that entries obtained via \"stdout\" or \"stderr\" of\nforked processes will contain credentials valid for a parent process (that initiated the\nconnection to systemd-journald).\n\nCOMM=, EXE=, CMDLINE=\nThe name, the executable path, and the command line of the process the journal entry\noriginates from.\n\nCAPEFFECTIVE=\nThe effective capabilities(7) of the process the journal entry originates from.\n\nAdded in version 206.\n\nAUDITSESSION=, AUDITLOGINUID=\nThe session and login UID of the process the journal entry originates from, as maintained\nby the kernel audit subsystem.\n\nSYSTEMDCGROUP=, SYSTEMDSLICE=, SYSTEMDUNIT=, SYSTEMDUSERUNIT=, SYSTEMDUSERSLICE=,\nSYSTEMDSESSION=, SYSTEMDOWNERUID=\nThe control group path in the systemd hierarchy, the systemd slice unit name, the systemd\nunit name, the unit name in the systemd user manager (if any), the systemd session ID (if\nany), and the owner UID of the systemd user unit or systemd session (if any) of the\nprocess the journal entry originates from.\n\nSELINUXCONTEXT=\nThe SELinux security context (label) of the process the journal entry originates from.\n\nSOURCEREALTIMETIMESTAMP=\nThe earliest trusted timestamp of the message, if any is known that is different from the\nreception time of the journal. This is the time in microseconds since the epoch UTC,\nformatted as a decimal string.\n\nBOOTID=\nThe kernel boot ID for the boot the message was generated in, formatted as a 128-bit\nhexadecimal string.\n\nMACHINEID=\nThe machine ID of the originating host, as available in machine-id(5).\n\nSYSTEMDINVOCATIONID=\nThe invocation ID for the runtime cycle of the unit the message was generated in, as\navailable to processes of the unit in $INVOCATIONID (see systemd.exec(5)).\n\nAdded in version 233.\n\nHOSTNAME=\nThe name of the originating host.\n\nTRANSPORT=\nHow the entry was received by the journal service. Valid transports are:\n\naudit\nfor those read from the kernel audit subsystem\n\nAdded in version 227.\n\ndriver\nfor internally generated messages\n\nAdded in version 205.\n\nsyslog\nfor those received via the local syslog socket with the syslog protocol\n\nAdded in version 205.\n\njournal\nfor those received via the native journal protocol\n\nAdded in version 205.\n\nstdout\nfor those read from a service's standard output or error output\n\nAdded in version 205.\n\nkernel\nfor those read from the kernel\n\nAdded in version 205.\n\nSTREAMID=\nOnly applies to \"TRANSPORT=stdout\" records: specifies a randomized 128-bit ID assigned\nto the stream connection when it was first created. This ID is useful to reconstruct\nindividual log streams from the log records: all log records carrying the same stream ID\noriginate from the same stream.\n\nAdded in version 235.\n\nLINEBREAK=\nOnly applies to \"TRANSPORT=stdout\" records: indicates that the log message in the\nstandard output/error stream was not terminated with a normal newline character (\"\\n\",\ni.e. ASCII 10). Specifically, when set this field is one of nul (in case the line was\nterminated by a NUL byte), line-max (in case the maximum log line length was reached, as\nconfigured with LineMax= in journald.conf(5)), eof (if this was the last log record of a\nstream and the stream ended without a final newline character), or pid-change (if the\nprocess which generated the log output changed in the middle of a line). Note that this\nrecord is not generated when a normal newline character was used for marking the log line\nend.\n\nAdded in version 235.\n\nNAMESPACE=\nIf this file was written by a systemd-journald instance managing a journal namespace that\nis not the default, this field contains the namespace identifier. See systemd-\njournald.service(8) for details about journal namespaces.\n\nAdded in version 245.\n\nRUNTIMESCOPE=\nA string field that specifies the runtime scope in which the message was logged. If\n\"initrd\", the log message was processed while the system was running inside the initrd.\nIf \"system\", the log message was generated after the system switched execution to the\nhost root filesystem.\n\nAdded in version 252.\n",
            "subsections": []
        },
        "KERNEL JOURNAL FIELDS": {
            "content": "Kernel fields are fields that are used by messages originating in the kernel and stored in\nthe journal.\n\nKERNELDEVICE=\nThe kernel device name. If the entry is associated to a block device, contains the major\nand minor numbers of the device node, separated by \":\" and prefixed by \"b\". Similarly for\ncharacter devices, but prefixed by \"c\". For network devices, this is the interface index\nprefixed by \"n\". For all other devices, this is the subsystem name prefixed by \"+\",\nfollowed by \":\", followed by the kernel device name.\n\nAdded in version 189.\n\nKERNELSUBSYSTEM=\nThe kernel subsystem name.\n\nAdded in version 189.\n\nUDEVSYSNAME=\nThe kernel device name as it shows up in the device tree below /sys/.\n\nAdded in version 189.\n\nUDEVDEVNODE=\nThe device node path of this device in /dev/.\n\nAdded in version 189.\n\nUDEVDEVLINK=\nAdditional symlink names pointing to the device node in /dev/. This field is frequently\nset more than once per entry.\n\nAdded in version 189.\n",
            "subsections": []
        },
        "FIELDS TO LOG ON BEHALF OF A DIFFERENT PROGRAM": {
            "content": "Fields in this section are used by programs to specify that they are logging on behalf of\nanother program or unit.\n\nFields used by the systemd-coredump coredump kernel helper:\n\nCOREDUMPUNIT=, COREDUMPUSERUNIT=\nUsed to annotate messages containing coredumps from system and session units. See\ncoredumpctl(1).\n\nAdded in version 198.\n\nPrivileged programs (currently UID 0) may attach OBJECTPID= to a message. This will instruct\nsystemd-journald to attach additional fields on behalf of the caller:\n\nOBJECTPID=PID\nPID of the program that this message pertains to.\n\nAdded in version 205.\n\nOBJECTUID=, OBJECTGID=, OBJECTCOMM=, OBJECTEXE=, OBJECTCMDLINE=, OBJECTAUDITSESSION=,\nOBJECTAUDITLOGINUID=, OBJECTSYSTEMDCGROUP=, OBJECTSYSTEMDSESSION=,\nOBJECTSYSTEMDOWNERUID=, OBJECTSYSTEMDUNIT=, OBJECTSYSTEMDUSERUNIT=\nThese are additional fields added automatically by systemd-journald. Their meaning is the\nsame as UID=, GID=, COMM=, EXE=, CMDLINE=, AUDITSESSION=, AUDITLOGINUID=,\nSYSTEMDCGROUP=, SYSTEMDSESSION=, SYSTEMDUNIT=, SYSTEMDUSERUNIT=, and\nSYSTEMDOWNERUID= as described above, except that the process identified by PID is\ndescribed, instead of the process which logged the message.\n\nAdded in version 205.\n",
            "subsections": []
        },
        "ADDRESS FIELDS": {
            "content": "During serialization into external formats, such as the Journal Export Format[1] or the\nJournal JSON Format[2], the addresses of journal entries are serialized into fields prefixed\nwith double underscores. Note that these are not proper fields when stored in the journal but\nfor addressing metadata of entries. They cannot be written as part of structured log entries\nvia calls such as sdjournalsend(3). They may also not be used as matches for\nsdjournaladdmatch(3).\n\nCURSOR=\nThe cursor for the entry. A cursor is an opaque text string that uniquely describes the\nposition of an entry in the journal and is portable across machines, platforms and\njournal files.\n\nREALTIMETIMESTAMP=\nThe wallclock time (CLOCKREALTIME) at the point in time the entry was received by the\njournal, in microseconds since the epoch UTC, formatted as a decimal string. This has\ndifferent properties from \"SOURCEREALTIMETIMESTAMP=\", as it is usually a bit later but\nmore likely to be monotonic.\n\nMONOTONICTIMESTAMP=\nThe monotonic time (CLOCKMONOTONIC) at the point in time the entry was received by the\njournal in microseconds, formatted as a decimal string. To be useful as an address for\nthe entry, this should be combined with the boot ID in \"BOOTID=\".\n\nSEQNUM=, SEQNUMID=\nThe sequence number (and associated sequence number ID) of this journal entry in the\njournal file it originates from. See sdjournalgetseqnum(3) for details.\n\nAdded in version 254.\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "systemd(1), systemd-journald.service(8), journalctl(1), journald.conf(5), sd-journal(3),\ncoredumpctl(1), systemd.directives(7)\n",
            "subsections": []
        },
        "NOTES": {
            "content": "1. Journal Export Format\nhttps://systemd.io/JOURNALEXPORTFORMATS#journal-export-format\n\n2. Journal JSON Format\nhttps://systemd.io/JOURNALEXPORTFORMATS#journal-json-format\n\nsystemd 255                                                                SYSTEMD.JOURNAL-FIELDS(7)",
            "subsections": []
        }
    },
    "summary": "systemd.journal-fields - Special journal fields",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "systemd",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/systemd/1/json"
        },
        {
            "name": "systemd-journald.service",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/systemd-journald.service/8/json"
        },
        {
            "name": "journalctl",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/journalctl/1/json"
        },
        {
            "name": "journald.conf",
            "section": "5",
            "url": "https://www.chedong.com/phpMan.php/man/journald.conf/5/json"
        },
        {
            "name": "sd-journal",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/sd-journal/3/json"
        },
        {
            "name": "coredumpctl",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/coredumpctl/1/json"
        },
        {
            "name": "systemd.directives",
            "section": "7",
            "url": "https://www.chedong.com/phpMan.php/man/systemd.directives/7/json"
        }
    ]
}