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<refentry id="systemd.journal-fields">

<refentryinfo>

<title>systemd.journal-fields</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>systemd.journal-fields</refentrytitle>

<manvolnum>7</manvolnum>

</refmeta>

<refnamediv>

<refname>systemd.journal-fields</refname>

<refpurpose>Special journal fields</refpurpose>

</refnamediv>

<refsect1>

<title>Description</title>

<para>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.</para>

</refsect1>

<refsect1>

<title>User Journal Fields</title>

<para>User fields are fields that are directly passed from clients

and stored in the journal.</para>

<variablelist class='journal-directives'>

<varlistentry>

<term><varname>MESSAGE=</varname></term>

<listitem>

<para>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 metadata.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>MESSAGE_ID=</varname></term>

<listitem>

<para>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 <command>journalctl

<option>--new-id</option></command>.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>PRIORITY=</varname></term>

<listitem>

<para>A priority value between 0 (<literal>emerg</literal>)

and 7 (<literal>debug</literal>) formatted as a decimal

string. This field is compatible with syslog's priority

concept.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>CODE_FILE=</varname></term>

<term><varname>CODE_LINE=</varname></term>

<term><varname>CODE_FUNC=</varname></term>

<listitem>

<para>The code location generating this message, if known.

Contains the source filename, the line number and the

function name.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>ERRNO=</varname></term>

<listitem>

<para>The low-level Unix error number causing this entry, if

any. Contains the numeric value of

<citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>

formatted as a decimal string.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>SYSLOG_FACILITY=</varname></term>

<term><varname>SYSLOG_IDENTIFIER=</varname></term>

<term><varname>SYSLOG_PID=</varname></term>

<listitem>

<para>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

<varname>program_invocation_short_name</varname> variable,

see

<citerefentry project='die-net'><refentrytitle>program_invocation_short_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>.)</para>

</listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Trusted Journal Fields</title>

<para>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.</para>

<variablelist class='journal-directives'>

<varlistentry>

<term><varname>_PID=</varname></term>

<term><varname>_UID=</varname></term>

<term><varname>_GID=</varname></term>

<listitem>

<para>The process, user, and group ID of the process the

journal entry originates from formatted as a decimal

string.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_COMM=</varname></term>

<term><varname>_EXE=</varname></term>

<term><varname>_CMDLINE=</varname></term>

<listitem>

<para>The name, the executable path, and the command line of

the process the journal entry originates from.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_CAP_EFFECTIVE=</varname></term>

<listitem>

<para>The effective

<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>

of the process the journal entry originates from.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_AUDIT_SESSION=</varname></term>

<term><varname>_AUDIT_LOGINUID=</varname></term>

<listitem>

<para>The session and login UID of the process the journal

entry originates from, as maintained by the kernel audit

subsystem.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_SYSTEMD_CGROUP=</varname></term>

<term><varname>_SYSTEMD_SESSION=</varname></term>

<term><varname>_SYSTEMD_UNIT=</varname></term>

<term><varname>_SYSTEMD_USER_UNIT=</varname></term>

<term><varname>_SYSTEMD_OWNER_UID=</varname></term>

<term><varname>_SYSTEMD_SLICE=</varname></term>

<listitem>

<para>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.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_SELINUX_CONTEXT=</varname></term>

<listitem>

<para>The SELinux security context (label) of the process

the journal entry originates from.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_SOURCE_REALTIME_TIMESTAMP=</varname></term>

<listitem>

<para>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.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_BOOT_ID=</varname></term>

<listitem>

<para>The kernel boot ID for the boot the message was

generated in, formatted as a 128-bit hexadecimal

string.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_MACHINE_ID=</varname></term>

<listitem>

<para>The machine ID of the originating host, as available

in

<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_HOSTNAME=</varname></term>

<listitem>

<para>The name of the originating host.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_TRANSPORT=</varname></term>

<listitem>

<para>How the entry was received by the journal service.

Valid transports are:

</para>

<variablelist>

<varlistentry>

<term>

<option>audit</option>

</term>

<listitem>

<para>for those read from the kernel audit subsystem

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

<option>driver</option>

</term>

<listitem>

<para>for internally generated messages

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

<option>syslog</option>

</term>

<listitem>

<para>for those received via the local syslog socket

with the syslog protocol

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

<option>journal</option>

</term>

<listitem>

<para>for those received via the native journal

protocol

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

<option>stdout</option>

</term>

<listitem>

<para>for those read from a service's standard output

or error output

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

<option>kernel</option>

</term>

<listitem>

<para>for those read from the kernel

</para>

</listitem>

</varlistentry>

</variablelist>

</listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Kernel Journal Fields</title>

<para>Kernel fields are fields that are used by messages

originating in the kernel and stored in the journal.</para>

<variablelist class='journal-directives'>

<varlistentry>

<term><varname>_KERNEL_DEVICE=</varname></term>

<listitem>

<para>The kernel device name. If the entry is associated to

a block device, the major and minor of the device node,

separated by <literal>:</literal> and prefixed by

<literal>b</literal>. Similar for character devices but

prefixed by <literal>c</literal>. For network devices, this

is the interface index prefixed by <literal>n</literal>. For

all other devices, this is the subsystem name prefixed by

<literal>+</literal>, followed by <literal>:</literal>,

followed by the kernel device name.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_KERNEL_SUBSYSTEM=</varname></term>

<listitem>

<para>The kernel subsystem name.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_UDEV_SYSNAME=</varname></term>

<listitem>

<para>The kernel device name as it shows up in the device

tree below <filename>/sys</filename>.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_UDEV_DEVNODE=</varname></term>

<listitem>

<para>The device node path of this device in

<filename>/dev</filename>.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>_UDEV_DEVLINK=</varname></term>

<listitem>

<para>Additional symlink names pointing to the device node

in <filename>/dev</filename>. This field is frequently set

more than once per entry.</para>

</listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Fields to log on behalf of a different program</title>

<para>Fields in this section are used by programs to specify that

they are logging on behalf of another program or unit.

</para>

<para>Fields used by the <command>systemd-coredump</command>

coredump kernel helper:

</para>

<variablelist class='journal-directives'>

<varlistentry>

<term><varname>COREDUMP_UNIT=</varname></term>

<term><varname>COREDUMP_USER_UNIT=</varname></term>

<listitem>

<para>Used to annotate messages containing coredumps from

system and session units. See

<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.

</para>

</listitem>

</varlistentry>

</variablelist>

<para>Privileged programs (currently UID 0) may attach

<varname>OBJECT_PID=</varname> to a message. This will instruct

<command>systemd-journald</command> to attach additional fields on

behalf of the caller:</para>

<variablelist class='journal-directives'>

<varlistentry>

<term><varname>OBJECT_PID=<replaceable>PID</replaceable></varname></term>

<listitem>

<para>PID of the program that this message pertains to.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>OBJECT_UID=</varname></term>

<term><varname>OBJECT_GID=</varname></term>

<term><varname>OBJECT_COMM=</varname></term>

<term><varname>OBJECT_EXE=</varname></term>

<term><varname>OBJECT_CMDLINE=</varname></term>

<term><varname>OBJECT_AUDIT_SESSION=</varname></term>

<term><varname>OBJECT_AUDIT_LOGINUID=</varname></term>

<term><varname>OBJECT_SYSTEMD_CGROUP=</varname></term>

<term><varname>OBJECT_SYSTEMD_SESSION=</varname></term>

<term><varname>OBJECT_SYSTEMD_OWNER_UID=</varname></term>

<term><varname>OBJECT_SYSTEMD_UNIT=</varname></term>

<term><varname>OBJECT_SYSTEMD_USER_UNIT=</varname></term>

<listitem>

<para>These are additional fields added automatically by

<command>systemd-journald</command>. Their meaning is the

same as

<varname>_UID=</varname>,

<varname>_GID=</varname>,

<varname>_COMM=</varname>,

<varname>_EXE=</varname>,

<varname>_CMDLINE=</varname>,

<varname>_AUDIT_SESSION=</varname>,

<varname>_AUDIT_LOGINUID=</varname>,

<varname>_SYSTEMD_CGROUP=</varname>,

<varname>_SYSTEMD_SESSION=</varname>,

<varname>_SYSTEMD_UNIT=</varname>,

<varname>_SYSTEMD_USER_UNIT=</varname>, and

<varname>_SYSTEMD_OWNER_UID=</varname>

as described above, except that the process identified by

<replaceable>PID</replaceable> is described, instead of the

process which logged the message.</para>

</listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Address Fields</title>

<para>During serialization into external formats, such as the

<ulink

url="http://www.freedesktop.org/wiki/Software/systemd/export">Journal

Export Format</ulink> or the <ulink

url="http://www.freedesktop.org/wiki/Software/systemd/json">Journal

JSON Format</ulink>, 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

<citerefentry><refentrytitle>sd_journal_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.

They may also not be used as matches for

<citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry></para>

<variablelist class='journal-directives'>

<varlistentry>

<term><varname>__CURSOR=</varname></term>

<listitem>

<para>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.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>__REALTIME_TIMESTAMP=</varname></term>

<listitem>

<para>The wallclock time

(<constant>CLOCK_REALTIME</constant>) 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

<literal>_SOURCE_REALTIME_TIMESTAMP=</literal>, as it is

usually a bit later but more likely to be monotonic.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><varname>__MONOTONIC_TIMESTAMP=</varname></term>

<listitem>

<para>The monotonic time

(<constant>CLOCK_MONOTONIC</constant>) 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

<literal>_BOOT_ID=</literal>.

</para>

</listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>