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man/daemon: recommend status notications, mention fd store

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This is just a small update. We probably should write a much longer document
that describes how to write a daemon in the XXI century.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2023-09-15 09:16:26 +02:00
parent bb8a3296e8
commit d73f8ff95f
1 changed files with 23 additions and 11 deletions
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34
man/daemon.xml
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@ -166,12 +166,22 @@
following:</para>
<orderedlist>
<listitem><para>If <constant>SIGTERM</constant> is received,
shut down the daemon and exit cleanly.</para></listitem>
<listitem><para>If applicable, the daemon should notify the init system about startup completion or
status updates via the
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
interface, in particular <varname>READY=1</varname> and <varname>STATUS=…</varname>.
</para></listitem>
<listitem><para>If <constant>SIGHUP</constant> is received,
reload the configuration files, if this
applies.</para></listitem>
<listitem><para>If <constant>SIGTERM</constant> is received, shut down the daemon and exit cleanly.
A <varname>STOPPING=1</varname> notification should be sent via
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
<listitem><para>If <constant>SIGHUP</constant> is received, reload the configuration files, if this
applies. This should be combined with notifications via
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>:
<varname>RELOADING=1</varname> and <varname>READY=1</varname>.
</para></listitem>
<listitem><para>Provide a correct exit code from the main
daemon process, as this is used by the init system to detect
@ -222,10 +232,10 @@
can be restarted without losing a single request. See below
for details.</para></listitem>
<listitem><para>If applicable, a daemon should notify the init
system about startup completion or status updates via the
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
interface.</para></listitem>
<listitem><para>If the service opens sockets or other files on it own, and those file descriptors
shall survive a restart, the daemon should store them in the service manager via
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry> with
<varname>FDSTORE=1</varname>..</para></listitem>
<listitem><para>Instead of using the
<function>syslog()</function> call to log directly to the
@ -243,8 +253,10 @@
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
<listitem><para>As new-style daemons are invoked without a controlling TTY (but as their own session
leaders) care should be taken to always specify `O_NOCTTY` on `open()` calls that possibly reference
a TTY device node, so that no controlling TTY is accidentally acquired.</para></listitem>
leaders) care should be taken to always specify <constant>O_NOCTTY</constant> on
<citerefentry><refentrytitle>open</refentrytitle><manvolnum>2</manvolnum></citerefentry>
calls that possibly reference a TTY device node, so that no controlling TTY is accidentally
acquired.</para></listitem>
</orderedlist>