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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<refentry id="systemd-journald.service">
<refentryinfo>
<title>systemd-journald.service</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-journald.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-journald.service</refname>
<refname>systemd-journald.socket</refname>
<refname>systemd-journald-dev-log.socket</refname>
<refname>systemd-journald-audit.socket</refname>
<refname>systemd-journald</refname>
<refpurpose>Journal service</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-journald.service</filename></para>
<para><filename>systemd-journald.socket</filename></para>
<para><filename>systemd-journald-dev-log.socket</filename></para>
<para><filename>systemd-journald-audit.socket</filename></para>
<para><filename>/usr/lib/systemd/systemd-journald</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-journald</filename> is a system service
that collects and stores logging data. It creates and maintains
structured, indexed journals based on logging information that is
received from a variety of sources:</para>
<itemizedlist>
<listitem><para>Kernel log messages, via kmsg</para></listitem>
<listitem><para>Simple system log messages, via the libc
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
call</para></listitem>
<listitem><para>Structured system log messages via the native
Journal API, see
<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry></para></listitem>
<listitem><para>Standard output and standard error of system
services</para></listitem>
<listitem><para>Audit records, via the audit
subsystem</para></listitem>
</itemizedlist>
<para>The daemon will implicitly collect numerous metadata fields
for each log messages in a secure and unfakeable way. See
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information about the collected metadata.
</para>
<para>Log data collected by the journal is primarily text-based
but can also include binary data where necessary. All objects
stored in the journal can be up to 2^64-1 bytes in size.</para>
<para>By default, the journal stores log data in
<filename>/run/log/journal/</filename>. Since
<filename>/run/</filename> is volatile, log data is lost at
reboot. To make the data persistent, it is sufficient to create
<filename>/var/log/journal/</filename> where
<filename>systemd-journald</filename> will then store the
data:</para>
<programlisting>mkdir -p /var/log/journal
systemd-tmpfiles --create --prefix /var/log/journal</programlisting>
<para><filename>systemd-journald</filename> will forward all
received log messages to the
<constant>AF_UNIX</constant>/<constant>SOCK_DGRAM</constant>
socket <filename>/run/systemd/journal/syslog</filename>, if it
exists, which may be used by Unix syslog daemons to process the
data further.</para>
<para>See
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for information about the configuration of this service.</para>
</refsect1>
<refsect1>
<title>Signals</title>
<variablelist>
<varlistentry>
<term>SIGUSR1</term>
<listitem><para>Request that journal data from
<filename>/run/</filename> is flushed to
<filename>/var/</filename> in order to make it persistent (if
this is enabled). This must be used after
<filename>/var/</filename> is mounted, as otherwise log data
from <filename>/run</filename> is never flushed to
<filename>/var</filename> regardless of the
configuration.</para></listitem>
</varlistentry>
<varlistentry>
<term>SIGUSR2</term>
<listitem><para>Request immediate rotation of the journal
files.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Kernel Command Line</title>
<para>A few configuration parameters from
<filename>journald.conf</filename> may be overridden on the kernel
command line:</para>
<variablelist class='kernel-commandline-options'>
<varlistentry>
<term><varname>systemd.journald.forward_to_syslog=</varname></term>
<term><varname>systemd.journald.forward_to_kmsg=</varname></term>
<term><varname>systemd.journald.forward_to_console=</varname></term>
<term><varname>systemd.journald.forward_to_wall=</varname></term>
<listitem><para>Enables/disables forwarding of collected log
messages to syslog, the kernel log buffer, the system console
or wall.
</para>
<para>See
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for information about these settings.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Access Control</title>
<para>Journal files are, by default, owned and readable by the
<literal>systemd-journal</literal> system group but are not
writable. Adding a user to this group thus enables her/him to read
the journal files.</para>
<para>By default, each logged in user will get her/his own set of
journal files in <filename>/var/log/journal/</filename>. These
files will not be owned by the user, however, in order to avoid
that the user can write to them directly. Instead, file system
ACLs are used to ensure the user gets read access only.</para>
<para>Additional users and groups may be granted access to journal
files via file system access control lists (ACL). Distributions
and administrators may choose to grant read access to all members
of the <literal>wheel</literal> and <literal>adm</literal> system
groups with a command such as the following:</para>
<programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
<para>Note that this command will update the ACLs both for
existing journal files and for future journal files created in the
<filename>/var/log/journal/</filename> directory.</para>
</refsect1>
<refsect1>
<title>Files</title>
<variablelist>
<varlistentry>
<term><filename>/etc/systemd/journald.conf</filename></term>
<listitem><para>Configure
<command>systemd-journald</command>
behavior. See
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
<term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
<term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
<term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
<listitem><para><command>systemd-journald</command> writes
entries to files in
<filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
or
<filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
with the <literal>.journal</literal> suffix. If the daemon is
stopped uncleanly, or if the files are found to be corrupted,
they are renamed using the <literal>.journal~</literal>
suffix, and <command>systemd-journald</command> starts writing
to a new file. <filename>/run</filename> is used when
<filename>/var/log/journal</filename> is not available, or
when <option>Storage=volatile</option> is set in the
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
configuration file.</para></listitem>
</varlistentry>
<varlistentry>
<term><filename>/dev/kmsg</filename></term>
<term><filename>/dev/log</filename></term>
<term><filename>/run/systemd/journal/dev-log</filename></term>
<term><filename>/run/systemd/journal/socket</filename></term>
<term><filename>/run/systemd/journal/stdout</filename></term>
<listitem><para>Sockets that
<command>systemd-journald</command> will listen on that are
visible in the file system. In addition to those, journald can
listen for audit events using netlink.</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>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
<command>pydoc systemd.journal</command>.
</para>
</refsect1>
</refentry>
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