man/systemd-journald.service.xml

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  24 <refentry id="systemd-journald.service">
  25
  26   <refentryinfo>
  27     <title>systemd-journald.service</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>systemd-journald.service</refentrytitle>
  42     <manvolnum>8</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>systemd-journald.service</refname>
  47     <refname>systemd-journald.socket</refname>
  48     <refname>systemd-journald-dev-log.socket</refname>
  49     <refname>systemd-journald-audit.socket</refname>
  50     <refname>systemd-journald</refname>
  51     <refpurpose>Journal service</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <para><filename>systemd-journald.service</filename></para>
  56     <para><filename>systemd-journald.socket</filename></para>
  57     <para><filename>systemd-journald-dev-log.socket</filename></para>
  58     <para><filename>systemd-journald-audit.socket</filename></para>
  59     <para><filename>/usr/lib/systemd/systemd-journald</filename></para>
  60   </refsynopsisdiv>
  61
  62   <refsect1>
  63     <title>Description</title>
  64
  65     <para><filename>systemd-journald</filename> is a system service
  66     that collects and stores logging data. It creates and maintains
  67     structured, indexed journals based on logging information that is
  68     received from a variety of sources:</para>
  69
  70     <itemizedlist>
  71       <listitem><para>Kernel log messages, via kmsg</para></listitem>
  72
  73       <listitem><para>Simple system log messages, via the libc
  74       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  75       call</para></listitem>
  76
  77       <listitem><para>Structured system log messages via the native
  78       Journal API, see
  79       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry></para></listitem>
  80
  81       <listitem><para>Standard output and standard error of system
  82       services</para></listitem>
  83
  84       <listitem><para>Audit records, via the audit
  85       subsystem</para></listitem>
  86     </itemizedlist>
  87
  88     <para>The daemon will implicitly collect numerous metadata fields
  89     for each log messages in a secure and unfakeable way. See
  90     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  91     for more information about the collected metadata.
  92     </para>
  93
  94     <para>Log data collected by the journal is primarily text-based
  95     but can also include binary data where necessary. All objects
  96     stored in the journal can be up to 2^64-1 bytes in size.</para>
  97
  98     <para>By default, the journal stores log data in
  99     <filename>/run/log/journal/</filename>. Since
 100     <filename>/run/</filename> is volatile, log data is lost at
 101     reboot. To make the data persistent, it is sufficient to create
 102     <filename>/var/log/journal/</filename> where
 103     <filename>systemd-journald</filename> will then store the
 104     data:</para>
 105
 106     <programlisting>mkdir -p /var/log/journal
 107 systemd-tmpfiles --create --prefix /var/log/journal</programlisting>
 108
 109     <para><filename>systemd-journald</filename> will forward all
 110     received log messages to the
 111     <constant>AF_UNIX</constant>/<constant>SOCK_DGRAM</constant>
 112     socket <filename>/run/systemd/journal/syslog</filename>, if it
 113     exists, which may be used by Unix syslog daemons to process the
 114     data further.</para>
 115
 116     <para>See
 117     <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 118     for information about the configuration of this service.</para>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>Signals</title>
 123
 124     <variablelist>
 125       <varlistentry>
 126         <term>SIGUSR1</term>
 127
 128         <listitem><para>Request that journal data from
 129         <filename>/run/</filename> is flushed to
 130         <filename>/var/</filename> in order to make it persistent (if
 131         this is enabled). This must be used after
 132         <filename>/var/</filename> is mounted, as otherwise log data
 133         from <filename>/run</filename> is never flushed to
 134         <filename>/var</filename> regardless of the
 135         configuration.</para></listitem>
 136       </varlistentry>
 137
 138       <varlistentry>
 139         <term>SIGUSR2</term>
 140
 141         <listitem><para>Request immediate rotation of the journal
 142         files.</para></listitem>
 143       </varlistentry>
 144     </variablelist>
 145   </refsect1>
 146
 147   <refsect1>
 148     <title>Kernel Command Line</title>
 149
 150     <para>A few configuration parameters from
 151     <filename>journald.conf</filename> may be overridden on the kernel
 152     command line:</para>
 153
 154     <variablelist class='kernel-commandline-options'>
 155       <varlistentry>
 156         <term><varname>systemd.journald.forward_to_syslog=</varname></term>
 157         <term><varname>systemd.journald.forward_to_kmsg=</varname></term>
 158         <term><varname>systemd.journald.forward_to_console=</varname></term>
 159         <term><varname>systemd.journald.forward_to_wall=</varname></term>
 160
 161         <listitem><para>Enables/disables forwarding of collected log
 162         messages to syslog, the kernel log buffer, the system console
 163         or wall.
 164         </para>
 165
 166         <para>See
 167         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 168         for information about these settings.</para>
 169         </listitem>
 170
 171       </varlistentry>
 172     </variablelist>
 173   </refsect1>
 174
 175   <refsect1>
 176     <title>Access Control</title>
 177
 178     <para>Journal files are, by default, owned and readable by the
 179     <literal>systemd-journal</literal> system group but are not
 180     writable. Adding a user to this group thus enables her/him to read
 181     the journal files.</para>
 182
 183     <para>By default, each logged in user will get her/his own set of
 184     journal files in <filename>/var/log/journal/</filename>. These
 185     files will not be owned by the user, however, in order to avoid
 186     that the user can write to them directly. Instead, file system
 187     ACLs are used to ensure the user gets read access only.</para>
 188
 189     <para>Additional users and groups may be granted access to journal
 190     files via file system access control lists (ACL). Distributions
 191     and administrators may choose to grant read access to all members
 192     of the <literal>wheel</literal> and <literal>adm</literal> system
 193     groups with a command such as the following:</para>
 194
 195     <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
 196
 197     <para>Note that this command will update the ACLs both for
 198     existing journal files and for future journal files created in the
 199     <filename>/var/log/journal/</filename> directory.</para>
 200   </refsect1>
 201
 202   <refsect1>
 203     <title>Files</title>
 204
 205     <variablelist>
 206       <varlistentry>
 207         <term><filename>/etc/systemd/journald.conf</filename></term>
 208
 209         <listitem><para>Configure
 210         <command>systemd-journald</command>
 211         behavior. See
 212         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 213         </para></listitem>
 214       </varlistentry>
 215
 216       <varlistentry>
 217         <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
 218         <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
 219         <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
 220         <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
 221
 222         <listitem><para><command>systemd-journald</command> writes
 223         entries to files in
 224         <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
 225         or
 226         <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
 227         with the <literal>.journal</literal> suffix. If the daemon is
 228         stopped uncleanly, or if the files are found to be corrupted,
 229         they are renamed using the <literal>.journal~</literal>
 230         suffix, and <command>systemd-journald</command> starts writing
 231         to a new file. <filename>/run</filename> is used when
 232         <filename>/var/log/journal</filename> is not available, or
 233         when <option>Storage=volatile</option> is set in the
 234         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 235         configuration file.</para></listitem>
 236       </varlistentry>
 237
 238       <varlistentry>
 239         <term><filename>/dev/kmsg</filename></term>
 240         <term><filename>/dev/log</filename></term>
 241         <term><filename>/run/systemd/journal/dev-log</filename></term>
 242         <term><filename>/run/systemd/journal/socket</filename></term>
 243         <term><filename>/run/systemd/journal/stdout</filename></term>
 244
 245         <listitem><para>Sockets and other paths that
 246         <command>systemd-journald</command> will listen on that are
 247         visible in the file system. In addition to these, journald can
 248         listen for audit events using netlink.</para></listitem>
 249       </varlistentry>
 250     </variablelist>
 251   </refsect1>
 252
 253   <refsect1>
 254     <title>See Also</title>
 255     <para>
 256       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 257       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 258       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 259       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 260       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 261       <citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 262       <citerefentry project='die-net'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 263       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
 264       <command>pydoc systemd.journal</command>.
 265     </para>
 266   </refsect1>
 267
 268 </refentry>