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950 lines
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950 lines
52 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="daemon">
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<refentryinfo>
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<title>daemon</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>daemon</refentrytitle>
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<manvolnum>7</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>daemon</refname>
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<refpurpose>Writing and Packaging System Daemons</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<para>A daemon is a service process that runs in the
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background and supervises the system or provides
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functionality to other processes. Traditionally,
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daemons are implemented following a scheme originating
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in SysV Unix. Modern daemons should follow a simpler
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yet more powerful scheme (here called "new-style"
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daemons), as implemented by
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. This
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manual page covers both schemes, and in
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particular includes recommendations for daemons that
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shall be included in the systemd init system.</para>
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<refsect2>
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<title>SysV Daemons</title>
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<para>When a traditional SysV daemon
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starts, it should execute the following steps
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as part of the initialization. Note that these
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steps are unnecessary for new-style daemons (see below),
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and should only be implemented if compatibility
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with SysV is essential.</para>
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<orderedlist>
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<listitem><para>Close all open file
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descriptors except STDIN, STDOUT,
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STDERR (i.e. the first three file
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descriptors 0, 1, 2). This ensures
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that no accidentally passed file
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descriptor stays around in the daemon
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process. On Linux this is best
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implemented by iterating through
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<filename>/proc/self/fd</filename>,
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with a fallback of iterating from file
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descriptor 3 to the value returned by
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<function>getrlimit()</function> for
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RLIMIT_NOFILE.</para></listitem>
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<listitem><para>Reset all signal
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handlers to their default. This is
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best done by iterating through the
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available signals up to the limit of
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_NSIG and resetting them to
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SIG_DFL.</para></listitem>
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<listitem><para>Reset the signal mask
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using
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<function>sigprocmask()</function>.</para></listitem>
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<listitem><para>Sanitize the
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environment block, removing or
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resetting environment variables that
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might negatively impact daemon
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runtime.</para></listitem>
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<listitem><para>Call <function>fork()</function>,
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to create a background
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process.</para></listitem>
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<listitem><para>In the child, call
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<function>setsid()</function> to
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detach from any terminal and create an
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independent session.</para></listitem>
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<listitem><para>In the child, call
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<function>fork()</function> again, to
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ensure the daemon can never re-acquire
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a terminal again.</para></listitem>
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<listitem><para>Call <function>exit()</function> in the
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first child, so that only the second
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child (the actual daemon process)
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stays around. This ensures that the
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daemon process is reparented to
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init/PID 1, as all daemons should
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be.</para></listitem>
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<listitem><para>In the daemon process,
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connect <filename>/dev/null</filename>
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to STDIN, STDOUT,
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STDERR.</para></listitem>
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<listitem><para>In the daemon process,
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reset the umask to 0, so that the file
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modes passed to <function>open()</function>, <function>mkdir()</function> and
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suchlike directly control the access
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mode of the created files and
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directories.</para></listitem>
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<listitem><para>In the daemon process,
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change the current directory to the
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root directory (/), in order to avoid
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that the daemon involuntarily
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blocks mount points from being
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unmounted.</para></listitem>
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<listitem><para>In the daemon process,
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write the daemon PID (as returned by
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<function>getpid()</function>) to a
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PID file, for example
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<filename>/var/run/foobar.pid</filename>
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(for a hypothetical daemon "foobar"),
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to ensure that the daemon cannot be
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started more than once. This must be
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implemented in race-free fashion so
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that the PID file is only updated when
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at the same time it is verified that
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the PID previously stored in the PID
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file no longer exists or belongs to a
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foreign process. Commonly some kind of
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file locking is employed to implement
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this logic.</para></listitem>
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<listitem><para>In the daemon process,
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drop privileges, if possible and
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applicable.</para></listitem>
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<listitem><para>From the daemon
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process notify the original process
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started that initialization is
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complete. This can be implemented via
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an unnamed pipe or similar
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communication channel that is created
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before the first
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<function>fork()</function> and hence
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available in both the original and the
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daemon process.</para></listitem>
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<listitem><para>Call
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<function>exit()</function> in the
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original process. The process that
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invoked the daemon must be able to
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rely that this
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<function>exit()</function> happens
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after initialization is complete and
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all external communication channels
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established and
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accessible.</para></listitem>
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</orderedlist>
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<para>The BSD <function>daemon()</function> function should not be
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used, as it implements only a subset of these steps.</para>
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<para>A daemon that needs to provide
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compatibility with SysV systems should
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implement the scheme pointed out
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above. However, it is recommended to make this
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behaviour optional and configurable via a
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command line argument, to ease debugging as
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well as to simplify integration into systems
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using systemd.</para>
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</refsect2>
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<refsect2>
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<title>New-Style Daemons</title>
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<para>Modern services for Linux should be
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implemented as new-style daemons. This makes it
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easier to supervise and control them at
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runtime and simplifies their
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implementation.</para>
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<para>For developing a new-style daemon none
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of the initialization steps recommended for
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SysV daemons need to be implemented. New-style
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init systems such as systemd make all of them
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redundant. Moreover, since some of these steps
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interfere with process monitoring, file
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descriptor passing and other functionality of
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the init system it is recommended not to
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execute them when run as new-style
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service.</para>
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<para>Note that new-style init systems
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guarantee execution of daemon processes in
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clean process contexts: it is guaranteed that
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the environment block is sanitized, that the
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signal handlers and mask is reset and that no
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left-over file descriptors are passed. Daemons
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will be executed in their own session, and
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STDIN/STDOUT/STDERR connected to
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<filename>/dev/null</filename> unless
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otherwise configured. The umask is reset.</para>
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<para>It is recommended for new-style daemons
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to implement the following:</para>
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<orderedlist>
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<listitem><para>If SIGTERM is
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received, shut down the daemon and
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exit cleanly.</para></listitem>
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<listitem><para>If SIGHUP is received,
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reload the configuration files, if
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this applies.</para></listitem>
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<listitem><para>Provide a correct exit
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code from the main daemon process, as
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this is used by the init system to
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detect service errors and problems. It
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is recommended to follow the exit code
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scheme as defined in the <ulink
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url="http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
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recommendations for SysV init
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scripts</ulink>.</para></listitem>
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<listitem><para>If possible and
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applicable expose the daemon's control
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interface via the D-Bus IPC system and
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grab a bus name as last step of
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initialization.</para></listitem>
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<listitem><para>For integration in
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systemd, provide a
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<filename>.service</filename> unit
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file that carries information about
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starting, stopping and otherwise
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maintaining the daemon. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details.</para></listitem>
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<listitem><para>As much as possible,
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rely on the init systemd's
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functionality to limit the access of
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the daemon to files, services and
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other resources. i.e. in the case of
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systemd, rely on systemd's resource
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limit control instead of implementing
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your own, rely on systemd's privilege
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dropping code instead of implementing
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it in the daemon, and similar. See
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the available
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controls.</para></listitem>
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<listitem><para>If D-Bus is used, make
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your daemon bus-activatable, via
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supplying a D-Bus service activation
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configuration file. This has multiple
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advantages: your daemon may be started
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lazily on-demand; it may be started in
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parallel to other daemons requiring it
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-- which maximizes parallelization and
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boot-up speed; your daemon can be
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restarted on failure, without losing
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any bus requests, as the bus queues
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requests for activatable services. See
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below for details.</para></listitem>
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<listitem><para>If your daemon
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provides services to other local
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processes or remote clients via a
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socket, it should be made
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socket-activatable following the
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scheme pointed out below. Like D-Bus
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activation this enables on-demand
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starting of services as well as it
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allows improved parallelization of
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service start-up. Also, for state-less
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protocols (such as syslog, DNS) a
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daemon implementing socket-based
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activation can be restarted without
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losing a single request. See below for
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details.</para></listitem>
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<listitem><para>If applicable a daemon
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should notify the init system about
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startup completion or status updates
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via the
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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interface.</para></listitem>
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<listitem><para>Instead of using the
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<function>syslog()</function> call to log directly to the
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system syslog service, a new-style daemon may
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choose to simply log to STDERR via
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<function>fprintf()</function>, which is then forwarded to
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syslog by the init system. If log
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priorities are necessary these can be
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encoded by prefixing individual log
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lines with strings like "<4>"
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(for log priority 4 "WARNING" in the
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syslog priority scheme), following a
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similar style as the Linux kernel's
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<function>printk()</function> priority system. In fact,
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using this style of logging also
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enables the init system to optionally
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direct all application logging to the
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kernel log buffer (kmsg), as
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accessible via
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<citerefentry><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>. This
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kind of logging may be enabled by
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setting
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<varname>StandardError=syslog</varname>
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in the service unit file. For details
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see
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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</orderedlist>
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<para>These recommendations are similar but
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not identical to the <ulink
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url="http://developer.apple.com/mac/library/documentation/MacOSX/Conceptual/BPSystemStartup/Articles/LaunchOnDemandDaemons.html#//apple_ref/doc/uid/TP40001762-104738">Apple
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MacOS X Daemon Requirements</ulink>.</para>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Activation</title>
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<para>New-style init systems provide multiple
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additional mechanisms to activate services, as
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detailed below. It is common that services are
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configured to be activated via more than one mechanism
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at the same time. An example for systemd:
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<filename>bluetoothd.service</filename> might get
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activated either when Bluetooth hardware is plugged
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in, or when an application accesses its programming
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interfaces via D-Bus. Or, a print server daemon might
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get activated when traffic arrives at an IPP port, or
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when a printer is plugged in, or when a file is queued
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in the printer spool directory. Even for services that
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are intended to be started on system bootup
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unconditionally it is a good idea to implement some of
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the various activation schemes outlined below, in
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order to maximize parallelization: if a daemon
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implements a D-Bus service or listening socket,
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implementing the full bus and socket activation scheme
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allows starting of the daemon with its clients in
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parallel (which speeds up boot-up), since all its
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communication channels are established already, and no
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request is lost because client requests will be queued
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by the bus system (in case of D-Bus) or the kernel (in
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case of sockets), until the activation is
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completed.</para>
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<refsect2>
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<title>Activation on Boot</title>
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<para>Old-style daemons are usually activated
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exclusively on boot (and manually by the
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administrator) via SysV init scripts, as
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detailed in the <ulink
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url="http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
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Linux Standard Base Core
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Specification</ulink>. This method of
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activation is supported ubiquitously on Linux
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init systems, both old-style and new-style
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systems. Among other issues SysV init scripts
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have the disadvantage of involving shell
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scripts in the boot process. New-style init
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systems generally employ updated versions of
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activation, both during boot-up and during
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runtime and using more minimal service
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description files.</para>
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<para>In systemd, if the developer or
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administrator wants to make sure a service or
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other unit is activated automatically on boot
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it is recommended to place a symlink to the
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unit file in the <filename>.wants/</filename>
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directory of either
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<filename>multi-user.target</filename> or
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<filename>graphical.target</filename>, which
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are normally used as boot targets at system
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startup. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details about the
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<filename>.wants/</filename> directories, and
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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for details about the two boot targets.</para>
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</refsect2>
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<refsect2>
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<title>Socket-Based Activation</title>
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<para>In order to maximize the possible
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parallelization and robustness and simplify
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configuration and development, it is
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recommended for all new-style daemons that
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communicate via listening sockets to employ
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socket-based activation. In a socket-based
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activation scheme the creation and binding of
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the listening socket as primary communication
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channel of daemons to local (and sometimes
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remote) clients is moved out of the daemon
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code and into the init system. Based on
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per-daemon configuration the init system
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installs the sockets and then hands them off
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to the spawned process as soon as the
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respective daemon is to be started.
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Optionally activation of the service can be
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delayed until the first inbound traffic
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arrives at the socket, to implement on-demand
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activation of daemons. However, the primary
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advantage of this scheme is that all providers
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and all consumers of the sockets can be
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started in parallel as soon as all sockets
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are established. In addition to that daemons
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can be restarted with losing only a minimal
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number of client transactions or even any
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client request at all (the latter is
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particularly true for state-less protocols,
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such as DNS or syslog), because the socket
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stays bound and accessible during the restart,
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and all requests are queued while the daemon
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cannot process them.</para>
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<para>New-style daemons which support socket
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activation must be able to receive their
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sockets from the init system, instead of of
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creating and binding them themselves. For
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details about the programming interfaces for
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this scheme provided by systemd see
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<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>. For
|
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details about porting existing daemons to
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socket-based activation see below. With
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|
minimal effort it is possible to implement
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socket-based activation in addition to
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traditional internal socket creation in the
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same codebase in order to support both
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new-style and old-style init systems from the
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same daemon binary.</para>
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<para>systemd implements socket-based
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activation via <filename>.socket</filename>
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units, which are described in
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>. When
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configuring socket units for socket-based
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activation it is essential that all listening
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sockets are pulled in by the special target
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unit <filename>sockets.target</filename>. It
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is recommended to place a
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<varname>WantedBy=sockets.target</varname>
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directive in the <literal>[Install]</literal>
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|
section, to automatically add such a
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dependency on installation of a socket
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unit. Unless
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<varname>DefaultDependencies=no</varname> is
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set the necessary ordering dependencies are
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implicitly created for all socket units. For
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more information about
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<filename>sockets.target</filename> see
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>. It
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|
is not necessary or recommended to place any
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additional dependencies on socket units (for
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|
example from
|
|
<filename>multi-user.target</filename> or
|
|
suchlike) when one is installed in
|
|
<filename>sockets.target</filename>.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Bus-Based Activation</title>
|
|
|
|
<para>When the D-Bus IPC system is used for
|
|
communication with clients, new-style daemons
|
|
should employ bus activation so that they are
|
|
automatically activated when a client
|
|
application accesses their IPC
|
|
interfaces. This is configured in D-Bus
|
|
service files (not to be confused with systemd
|
|
service unit files!). To ensure that D-Bus
|
|
uses systemd to start-up and maintain the
|
|
daemon use the
|
|
<varname>SystemdService=</varname> directive
|
|
in these service files, to configure the
|
|
matching systemd service for a D-Bus
|
|
service. e.g.: for a D-Bus service whose D-Bus
|
|
activation file is named
|
|
<filename>org.freedesktop.RealtimeKit.service</filename>,
|
|
make sure to set
|
|
<varname>SystemdService=rtkit-daemon.service</varname>
|
|
in that file, to bind it to the systemd
|
|
service
|
|
<filename>rtkit-daemon.service</filename>. This
|
|
is needed to make sure that the daemon is
|
|
started in a race-free fashion when activated
|
|
via multiple mechanisms simultaneously.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Device-Based Activation</title>
|
|
|
|
<para>Often, daemons that manage a particular
|
|
type of hardware should be activated only when
|
|
the hardware of the respective kind is plugged
|
|
in or otherwise becomes available. In a
|
|
new-style init system it is possible to bind
|
|
activation to hardware plug/unplug events. In
|
|
systemd, kernel devices appearing in the
|
|
sysfs/udev device tree can be exposed as units
|
|
if they are tagged with the string
|
|
"<literal>systemd</literal>". Like any other
|
|
kind of unit they may then pull in other units
|
|
when activated (i.e. Plugged in) and thus
|
|
implement device-based activation. Systemd
|
|
dependencies may be encoded in the udev
|
|
database via the
|
|
<varname>SYSTEMD_WANTS=</varname>
|
|
property. See
|
|
<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details. Often it is nicer to pull in
|
|
services from devices only indirectly via
|
|
dedicated targets. Example: instead of pulling
|
|
in <filename>bluetoothd.service</filename>
|
|
from all the various bluetooth dongles and
|
|
other hardware available, pull in
|
|
bluetooth.target from them and
|
|
<filename>bluetoothd.service</filename> from
|
|
that target. This provides for nicer
|
|
abstraction and gives administrators the
|
|
option to enable
|
|
<filename>bluetoothd.service</filename> via
|
|
controlling a
|
|
<filename>bluetooth.target.wants/</filename>
|
|
symlink uniformly with a command like
|
|
<command>enable</command> of
|
|
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
instead of manipulating the udev
|
|
ruleset.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Path-Based Activation</title>
|
|
|
|
<para>Often, runtime of daemons processing
|
|
spool files or directories (such as a printing
|
|
system) can be delayed until these file system
|
|
objects change state, or become
|
|
non-empty. New-style init systems provide a
|
|
way to bind service activation to file system
|
|
changes. systemd implements this scheme via
|
|
path-based activation configured in
|
|
<filename>.path</filename> units, as outlined
|
|
in
|
|
<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Timer-Based Activation</title>
|
|
|
|
<para>Some daemons that implement clean-up
|
|
jobs that are intended to be executed in
|
|
regular intervals benefit from timer-based
|
|
activation. In systemd, this is implemented
|
|
via <filename>.timer</filename> units, as
|
|
described in
|
|
<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Other Forms of Activation</title>
|
|
|
|
<para>Other forms of activation have been
|
|
suggested and implemented in some
|
|
systems. However, often there are simpler or
|
|
better alternatives, or they can be put
|
|
together of combinations of the schemes
|
|
above. Example: sometimes it appears useful to
|
|
start daemons or <filename>.socket</filename>
|
|
units when a specific IP address is configured
|
|
on a network interface, because network
|
|
sockets shall be bound to the
|
|
address. However, an alternative to implement
|
|
this is by utilizing the Linux IP_FREEBIND
|
|
socket option, as accessible via
|
|
<varname>FreeBind=yes</varname> in systemd
|
|
socket files (see
|
|
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details). This option, when enabled,
|
|
allows sockets to be bound to a non-local, not
|
|
configured IP address, and hence allows
|
|
bindings to a particular IP address before it
|
|
actually becomes available, making such an
|
|
explicit dependency to the configured address
|
|
redundant. Another often suggested trigger for
|
|
service activation is low system
|
|
load. However, here too, a more convincing
|
|
approach might be to make proper use of
|
|
features of the operating system: in
|
|
particular, the CPU or IO scheduler of
|
|
Linux. Instead of scheduling jobs from
|
|
userspace based on monitoring the OS
|
|
scheduler, it is advisable to leave the
|
|
scheduling of processes to the OS scheduler
|
|
itself. systemd provides fine-grained access
|
|
to the CPU and IO schedulers. If a process
|
|
executed by the init system shall not
|
|
negatively impact the amount of CPU or IO
|
|
bandwidth available to other processes, it
|
|
should be configured with
|
|
<varname>CPUSchedulingPolicy=idle</varname>
|
|
and/or
|
|
<varname>IOSchedulingClass=idle</varname>. Optionally,
|
|
this may be combined with timer-based
|
|
activation to schedule background jobs during
|
|
runtime and with minimal impact on the system,
|
|
and remove it from the boot phase
|
|
itself.</para>
|
|
</refsect2>
|
|
|
|
</refsect1>
|
|
<refsect1>
|
|
<title>Integration with Systemd</title>
|
|
|
|
<refsect2>
|
|
<title>Writing Systemd Unit Files</title>
|
|
|
|
<para>When writing systemd unit files, it is
|
|
recommended to consider the following
|
|
suggestions:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>If possible do not use
|
|
the <varname>Type=forking</varname>
|
|
setting in service files. But if you
|
|
do, make sure to set the PID file path
|
|
using <varname>PIDFile=</varname>. See
|
|
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details.</para></listitem>
|
|
|
|
<listitem><para>If your daemon
|
|
registers a D-Bus name on the bus,
|
|
make sure to use
|
|
<varname>Type=dbus</varname> in the
|
|
service file if
|
|
possible.</para></listitem>
|
|
|
|
<listitem><para>Make sure to set a
|
|
good human-readable description string
|
|
with
|
|
<varname>Description=</varname>.</para></listitem>
|
|
|
|
<listitem><para>Do not disable
|
|
<varname>DefaultDependencies=</varname>,
|
|
unless you really know what you do and
|
|
your unit is involved in early boot or
|
|
late system shutdown.</para></listitem>
|
|
|
|
<listitem><para>Normally, little if
|
|
any dependencies should need to
|
|
be defined explicitly. However, if you
|
|
do configure explicit dependencies, only refer to
|
|
unit names listed on
|
|
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
or names introduced by your own
|
|
package to keep the unit file
|
|
operating
|
|
system-independent.</para></listitem>
|
|
|
|
<listitem><para>Make sure to include
|
|
an <literal>[Install]</literal>
|
|
section including installation
|
|
information for the unit file. See
|
|
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details. To activate your service
|
|
on boot make sure to add a
|
|
<varname>WantedBy=multi-user.target</varname>
|
|
or
|
|
<varname>WantedBy=graphical.target</varname>
|
|
directive. To activate your socket on
|
|
boot, make sure to add
|
|
<varname>WantedBy=sockets.target</varname>. Usually
|
|
you also want to make sure that when
|
|
your service is installed your socket
|
|
is installed too, hence add
|
|
<varname>Also=foo.socket</varname> in
|
|
your service file
|
|
<filename>foo.service</filename>, for
|
|
a hypothetical program
|
|
<filename>foo</filename>.</para></listitem>
|
|
|
|
</orderedlist>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Installing Systemd Service Files</title>
|
|
|
|
<para>At the build installation time
|
|
(e.g. <command>make install</command> during
|
|
package build) packages are recommended to
|
|
install their systemd unit files in the
|
|
directory returned by <command>pkg-config
|
|
systemd
|
|
--variable=systemdsystemunitdir</command> (for
|
|
system services), resp. <command>pkg-config
|
|
systemd
|
|
--variable=systemduserunitdir</command>
|
|
(for user services). This will make the
|
|
services available in the system on explicit
|
|
request but not activate them automatically
|
|
during boot. Optionally, during package
|
|
installation (e.g. <command>rpm -i</command>
|
|
by the administrator) symlinks should be
|
|
created in the systemd configuration
|
|
directories via the <command>enable</command>
|
|
command of the
|
|
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
tool, to activate them automatically on
|
|
boot.</para>
|
|
|
|
<para>Packages using
|
|
<citerefentry><refentrytitle>autoconf</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
are recommended to use a configure script
|
|
excerpt like the following to determine the
|
|
unit installation path during source
|
|
configuration:</para>
|
|
|
|
<programlisting>PKG_PROG_PKG_CONFIG
|
|
AC_ARG_WITH([systemdsystemunitdir],
|
|
AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [Directory for systemd service files]),
|
|
[], [with_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)])
|
|
if test "x$with_systemdsystemunitdir" != xno; then
|
|
AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])
|
|
fi
|
|
AM_CONDITIONAL(HAVE_SYSTEMD, [test -n "$with_systemdsystemunitdir" -a "x$with_systemdsystemunitdir" != xno ])</programlisting>
|
|
|
|
<para>This snippet allows automatic
|
|
installation of the unit files on systemd
|
|
machines, and optionally allows their
|
|
installation even on machines lacking
|
|
systemd. (Modification of this snippet for the
|
|
user unit directory is left as an exercise for the
|
|
reader.)</para>
|
|
|
|
<para>Additionally, to ensure that
|
|
<command>make distcheck</command> continues to
|
|
work, it is recommended to add the following
|
|
to the top-level <filename>Makefile.am</filename>
|
|
file in
|
|
<citerefentry><refentrytitle>automake</refentrytitle><manvolnum>1</manvolnum></citerefentry>-based
|
|
projects:</para>
|
|
|
|
<programlisting>DISTCHECK_CONFIGURE_FLAGS = \
|
|
--with-systemdsystemunitdir=$$dc_install_base/$(systemdsystemunitdir)</programlisting>
|
|
|
|
<para>Finally, unit files should be installed in the system with an automake excerpt like the following:</para>
|
|
|
|
<programlisting>if HAVE_SYSTEMD
|
|
systemdsystemunit_DATA = \
|
|
foobar.socket \
|
|
foobar.service
|
|
endif</programlisting>
|
|
|
|
<para>In the
|
|
<citerefentry><refentrytitle>rpm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
|
|
<filename>.spec</filename> file use snippets
|
|
like the following to enable/disable the
|
|
service during
|
|
installation/deinstallation. This makes use of
|
|
the RPM macros shipped along systemd. Consult
|
|
the packaging guidelines of your distribution
|
|
for details and the equivalent for other
|
|
package managers.</para>
|
|
|
|
<para>At the top of the file:</para>
|
|
|
|
<programlisting>BuildRequires: systemd
|
|
%{?systemd_requires}</programlisting>
|
|
|
|
<para>And as scriptlets, further down:</para>
|
|
|
|
<programlisting>%post
|
|
%systemd_post foobar.service foobar.socket
|
|
|
|
%preun
|
|
%systemd_preun foobar.service foobar.socket
|
|
|
|
%postun
|
|
%systemd_postun</programlisting>
|
|
|
|
<para>If the service shall be restarted during
|
|
upgrades replace the
|
|
<literal>%postun</literal> scriptlet above
|
|
with the following:</para>
|
|
|
|
<programlisting>%postun
|
|
%systemd_postun_with_restart foobar.service</programlisting>
|
|
|
|
<para>Note that
|
|
<literal>%systemd_post</literal> and
|
|
<literal>%systemd_preun</literal> expect the
|
|
names of all units that are installed/removed
|
|
as arguments, separated by
|
|
spaces. <literal>%systemd_postun</literal>
|
|
expects no
|
|
arguments. <literal>%systemd_postun_with_restart</literal>
|
|
expects the units to restart as
|
|
arguments.</para>
|
|
|
|
<para>To facilitate upgrades from a package
|
|
version that shipped only SysV init scripts to
|
|
a package version that ships both a SysV init
|
|
script and a native systemd service file, use
|
|
a fragment like the following:</para>
|
|
|
|
<programlisting>%triggerun -- foobar < 0.47.11-1
|
|
if /sbin/chkconfig --level 5 foobar ; then
|
|
/bin/systemctl --no-reload enable foobar.service foobar.socket >/dev/null 2>&1 || :
|
|
fi</programlisting>
|
|
|
|
<para>Where 0.47.11-1 is the first package
|
|
version that includes the native unit
|
|
file. This fragment will ensure that the first
|
|
time the unit file is installed it will be
|
|
enabled if and only if the SysV init script is
|
|
enabled, thus making sure that the enable
|
|
status is not changed. Note that
|
|
<command>chkconfig</command> is a command
|
|
specific to Fedora which can be used to check
|
|
whether a SysV init script is enabled. Other
|
|
operating systems will have to use different
|
|
commands here.</para>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Porting Existing Daemons</title>
|
|
|
|
<para>Since new-style init systems such as systemd are
|
|
compatible with traditional SysV init systems it is
|
|
not strictly necessary to port existing daemons to the
|
|
new style. However doing so offers additional
|
|
functionality to the daemons as well as simplifying
|
|
integration into new-style init systems.</para>
|
|
|
|
<para>To port an existing SysV compatible daemon the
|
|
following steps are recommended:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>If not already implemented,
|
|
add an optional command line switch to the
|
|
daemon to disable daemonization. This is
|
|
useful not only for using the daemon in
|
|
new-style init systems, but also to ease
|
|
debugging.</para></listitem>
|
|
|
|
<listitem><para>If the daemon offers
|
|
interfaces to other software running on the
|
|
local system via local AF_UNIX sockets,
|
|
consider implementing socket-based activation
|
|
(see above). Usually a minimal patch is
|
|
sufficient to implement this: Extend the
|
|
socket creation in the daemon code so that
|
|
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
is checked for already passed sockets
|
|
first. If sockets are passed (i.e. when
|
|
<function>sd_listen_fds()</function> returns a
|
|
positive value), skip the socket creation step
|
|
and use the passed sockets. Secondly, ensure
|
|
that the file-system socket nodes for local
|
|
AF_UNIX sockets used in the socket-based
|
|
activation are not removed when the daemon
|
|
shuts down, if sockets have been
|
|
passed. Third, if the daemon normally closes
|
|
all remaining open file descriptors as part of
|
|
its initialization, the sockets passed from
|
|
the init system must be spared. Since
|
|
new-style init systems guarantee that no
|
|
left-over file descriptors are passed to
|
|
executed processes, it might be a good choice
|
|
to simply skip the closing of all remaining
|
|
open file descriptors if sockets are
|
|
passed.</para></listitem>
|
|
|
|
<listitem><para>Write and install a systemd
|
|
unit file for the service (and the sockets if
|
|
socket-based activation is used, as well as a
|
|
path unit file, if the daemon processes a
|
|
spool directory), see above for
|
|
details.</para></listitem>
|
|
|
|
<listitem><para>If the daemon exposes
|
|
interfaces via D-Bus, write and install a
|
|
D-Bus activation file for the service, see
|
|
above for details.</para></listitem>
|
|
</orderedlist>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|