path: root/nixos/doc/manual/administration/logging.xml

<chapter xmlns="http://docbook.org/ns/docbook"
        xmlns:xlink="http://www.w3.org/1999/xlink"
        xmlns:xi="http://www.w3.org/2001/XInclude"
        version="5.0"
        xml:id="sec-logging">

<title>Logging</title>

<para>System-wide logging is provided by systemd’s
<emphasis>journal</emphasis>, which subsumes traditional logging
daemons such as syslogd and klogd.  Log entries are kept in binary
files in <filename>/var/log/journal/</filename>.  The command
<literal>journalctl</literal> allows you to see the contents of the
journal.  For example,

<screen>
$ journalctl -b
</screen>

shows all journal entries since the last reboot.  (The output of
<command>journalctl</command> is piped into <command>less</command> by
default.)  You can use various options and match operators to restrict
output to messages of interest.  For instance, to get all messages
from PostgreSQL:

<screen>
$ journalctl -u postgresql.service
-- Logs begin at Mon, 2013-01-07 13:28:01 CET, end at Tue, 2013-01-08 01:09:57 CET. --
...
Jan 07 15:44:14 hagbard postgres[2681]: [2-1] LOG:  database system is shut down
-- Reboot --
Jan 07 15:45:10 hagbard postgres[2532]: [1-1] LOG:  database system was shut down at 2013-01-07 15:44:14 CET
Jan 07 15:45:13 hagbard postgres[2500]: [1-1] LOG:  database system is ready to accept connections
</screen>

Or to get all messages since the last reboot that have at least a
“critical” severity level:

<screen>
$ journalctl -b -p crit
Dec 17 21:08:06 mandark sudo[3673]: pam_unix(sudo:auth): auth could not identify password for [alice]
Dec 29 01:30:22 mandark kernel[6131]: [1053513.909444] CPU6: Core temperature above threshold, cpu clock throttled (total events = 1)
</screen>

</para>

<para>The system journal is readable by root and by users in the
<literal>wheel</literal> and <literal>systemd-journal</literal>
groups.  All users have a private journal that can be read using
<command>journalctl</command>.</para>

</chapter>