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Diffstat (limited to 'man/systemd-journald.service.xml')
| -rw-r--r-- | man/systemd-journald.service.xml | 54 |
1 files changed, 48 insertions, 6 deletions
diff --git a/man/systemd-journald.service.xml b/man/systemd-journald.service.xml index 2810638bc2..559ef1090a 100644 --- a/man/systemd-journald.service.xml +++ b/man/systemd-journald.service.xml @@ -70,19 +70,18 @@ <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> + <listitem><para>Simple system log messages, via the <filename>libc</filename> <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>Standard output and standard error of service units. For further details see + below.</para></listitem> - <listitem><para>Audit records, via the audit - subsystem</para></listitem> + <listitem><para>Audit records, originating from the kernel audit subsystem</para></listitem> </itemizedlist> <para>The daemon will implicitly collect numerous metadata fields @@ -112,6 +111,49 @@ systemd-tmpfiles --create --prefix /var/log/journal</programlisting> </refsect1> <refsect1> + <title>Stream logging</title> + + <para>The systemd service manager invokes all service processes with standard output and standard error connected + to the journal by default. This behaviour may be altered via the + <varname>StandardOutput=</varname>/<varname>StandardError=</varname> unit file settings, see + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The + journal converts the log byte stream received this way into individual log records, splitting the stream at newline + (<literal>\n</literal>, ASCII <constant>10</constant>) and <constant>NUL</constant> bytes.</para> + + <para>If <filename>systemd-journald.service</filename> is stopped, the stream connections associated with all + services are terminated. Further writes to those streams by the service will result in <constant>EPIPE</constant> + errors. In order to react gracefully in this case it is recommended that programs logging to standard output/error + ignore such errors. If the the <constant>SIGPIPE</constant> UNIX signal handler is not blocked or turned off, such + write attempts will also result in such process signals being generated, see + <citerefentry><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>. To mitigate this issue, + systemd service manager explicitly turns off the <constant>SIGPIPE</constant> signal for all invoked processes by + default (this may be changed for each unit individually via the <varname>IgnoreSIGPIPE=</varname> option, see + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for + details). After the standard output/standard error streams have been terminated they may not be recovered until the + services they are associated with are restarted. Note that during normal operation, + <filename>systemd-journald.service</filename> stores copies of the file descriptors for those streams in the + service manager. If <filename>systemd-journald.service</filename> is restarted using <command>systemctl + restart</command> or equivalent operation instead of a pair of separate <command>systemctl stop</command> and + <command>systemctl start</command> commands (or equivalent operations), these stream connections are not terminated + and survive the restart. It is thus safe to restart <filename>systemd-journald.service</filename>, but stopping it + is not recommended.</para> + + <para>Note that the log record metadata for records transferred via such standard output/error streams reflect the + metadata of the peer the stream was originally created for. If the stream connection is passed on to other + processes (such as further child processes forked off the main service process), the log records will not reflect + their metadata, but will continue to describe the original process. This is different from the other logging + transports listed above, which are inherently record based and where the metadata is always associated with the + individual record.</para> + + <para>In addition to the the implicit standard output/error logging of services, stream logging is also available + via the <citerefentry><refentrytitle>systemd-cat</refentrytitle><manvolnum>1</manvolnum></citerefentry> command + line tool.</para> + + <para> Currently, the number of parallel log streams <filename>systemd-journald</filename> will accept is limited + to 4096.</para> + </refsect1> + + <refsect1> <title>Signals</title> <variablelist> |