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