732 lines
36 KiB
XML
732 lines
36 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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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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</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 background
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and supervises the system or provides functionality to other
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processes. Traditionally, daemons are implemented following a
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scheme originating in SysV Unix. Modern daemons should follow a
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simpler 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>.
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This manual page covers both schemes, and in particular includes
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recommendations for daemons that shall be included in the systemd
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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 starts, it should execute
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the following steps as part of the initialization. Note that
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these steps are unnecessary for new-style daemons (see below),
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and should only be implemented if compatibility with SysV is
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essential.</para>
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<orderedlist>
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<listitem><para>Close all open file descriptors except
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standard input, output, and error (i.e. the first three file
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descriptors 0, 1, 2). This ensures that no accidentally passed
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file descriptor stays around in the daemon process. On Linux,
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this is best implemented by iterating through
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<filename>/proc/self/fd</filename>, with a fallback of
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iterating from file descriptor 3 to the value returned by
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<function>getrlimit()</function> for
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<constant>RLIMIT_NOFILE</constant>. </para></listitem>
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<listitem><para>Reset all signal handlers to their default.
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This is best done by iterating through the available signals
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up to the limit of <constant>_NSIG</constant> and resetting
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them to <constant>SIG_DFL</constant>.</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 environment block, removing or
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resetting environment variables that might negatively impact
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daemon runtime.</para></listitem>
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<listitem><para>Call <function>fork()</function>, to create a
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background process.</para></listitem>
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<listitem><para>In the child, call
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<function>setsid()</function> to detach from any terminal and
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create an independent session.</para></listitem>
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<listitem><para>In the child, call <function>fork()</function> again, to ensure that the daemon can
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never re-acquire a terminal again. (This relevant if the program — and all its dependencies — does
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not carefully specify `O_NOCTTY` on each and every single `open()` call that might potentially open a
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TTY device node.)</para></listitem>
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<listitem><para>Call <function>exit()</function> in the first
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child, so that only the second child (the actual daemon
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process) stays around. This ensures that the daemon process is
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re-parented to init/PID 1, as all daemons should
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be.</para></listitem>
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<listitem><para>In the daemon process, connect
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<filename>/dev/null</filename> to standard input, output, and
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error.</para></listitem>
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<listitem><para>In the daemon process, reset the umask to 0,
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so that the file modes passed to <function>open()</function>,
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<function>mkdir()</function> and suchlike directly control the
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access mode of the created files and
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directories.</para></listitem>
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<listitem><para>In the daemon process, change the current
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directory to the root directory (/), in order to avoid that
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the daemon involuntarily blocks mount points from being
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unmounted.</para></listitem>
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<listitem><para>In the daemon process, write the daemon PID
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(as returned by <function>getpid()</function>) to a PID file,
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for example <filename index='false'>/run/foobar.pid</filename> (for a
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hypothetical daemon "foobar") to ensure that the daemon cannot
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be started more than once. This must be implemented in
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race-free fashion so that the PID file is only updated when it
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is verified at the same time that the PID previously stored in
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the PID file no longer exists or belongs to a foreign
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process.</para></listitem>
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<listitem><para>In the daemon process, drop privileges, if
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possible and applicable.</para></listitem>
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<listitem><para>From the daemon process, notify the original
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process started that initialization is complete. This can be
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implemented via an unnamed pipe or similar communication
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channel that is created before the first
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<function>fork()</function> and hence available in both the
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original and the daemon process.</para></listitem>
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<listitem><para>Call <function>exit()</function> in the
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original process. The process that invoked the daemon must be
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able to rely on that this <function>exit()</function> happens
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after initialization is complete and all external
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communication channels are 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
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be used, as it implements only a subset of these steps.</para>
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<para>A daemon that needs to provide compatibility with SysV
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systems should implement the scheme pointed out above. However,
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it is recommended to make this behavior optional and
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configurable via a command line argument to ease debugging as
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well as to simplify integration into systems using
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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 implemented as
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new-style daemons. This makes it easier to supervise and control
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them at runtime and simplifies their implementation.</para>
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<para>For developing a new-style daemon, none of the
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initialization steps recommended for SysV daemons need to be
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implemented. New-style init systems such as systemd make all of
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them redundant. Moreover, since some of these steps interfere
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with process monitoring, file descriptor passing and other
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functionality of the init system, it is recommended not to
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execute them when run as new-style service.</para>
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<para>Note that new-style init systems guarantee execution of daemon processes in a clean process context: it is
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guaranteed that the environment block is sanitized, that the signal handlers and mask is reset and that no
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left-over file descriptors are passed. Daemons will be executed in their own session, with standard input
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connected to <filename>/dev/null</filename> and standard output/error connected to the
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<citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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logging service, unless otherwise configured. The umask is reset.
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</para>
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<para>It is recommended for new-style daemons to implement the
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following:</para>
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<orderedlist>
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<listitem><para>If <constant>SIGTERM</constant> is received,
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shut down the daemon and exit cleanly.</para></listitem>
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<listitem><para>If <constant>SIGHUP</constant> is received,
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reload the configuration files, if this
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applies.</para></listitem>
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<listitem><para>Provide a correct exit code from the main
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daemon process, as this is used by the init system to detect
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service errors and problems. It is recommended to follow the
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exit code scheme as defined in the <ulink
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url="http://refspecs.linuxbase.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 applicable, expose the
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daemon's control interface via the D-Bus IPC system and grab a
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bus name as last step of initialization.</para></listitem>
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<listitem><para>For integration in systemd, provide a
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<filename>.service</filename> unit file that carries
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information about starting, stopping and otherwise maintaining
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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, rely on the init system's
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functionality to limit the access of the daemon to files,
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services and other resources, i.e. in the case of systemd,
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rely on systemd's resource limit control instead of
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implementing your own, rely on systemd's privilege dropping
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code instead of implementing it in the daemon, and similar.
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See
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the available controls.</para></listitem>
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<listitem><para>If D-Bus is used, make your daemon
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bus-activatable by supplying a D-Bus service activation
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configuration file. This has multiple advantages: your daemon
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may be started lazily on-demand; it may be started in parallel
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to other daemons requiring it — which maximizes
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parallelization and boot-up speed; your daemon can be
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restarted on failure without losing any bus requests, as the
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bus queues requests for activatable services. See below for
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details.</para></listitem>
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<listitem><para>If your daemon provides services to other
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local processes or remote clients via a socket, it should be
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made socket-activatable following the scheme pointed out
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below. Like D-Bus activation, this enables on-demand starting
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of services as well as it allows improved parallelization of
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service start-up. Also, for state-less protocols (such as
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syslog, DNS), a daemon implementing socket-based activation
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can be restarted without losing a single request. See below
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for details.</para></listitem>
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<listitem><para>If applicable, a daemon should notify the init
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system about startup completion or status updates 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 choose to simply
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log to standard error via <function>fprintf()</function>,
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which is then forwarded to syslog by the init system. If log
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levels are necessary, these can be encoded by prefixing
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individual log lines with strings like
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<literal><4></literal> (for log level 4 "WARNING" in the
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syslog priority scheme), following a similar style as the
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Linux kernel's <function>printk()</function> level system. For
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details, see
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</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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<listitem><para>As new-style daemons are invoked without a controlling TTY (but as their own session
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leaders) care should be taken to always specify `O_NOCTTY` on `open()` calls that possibly reference
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a TTY device node, so that no controlling TTY is accidentally acquired.</para></listitem>
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</orderedlist>
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<para>These recommendations are similar but not identical to the
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<ulink
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url="https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html">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 additional
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mechanisms to activate services, as detailed below. It is common
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that services are configured to be activated via more than one
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mechanism at the same time. An example for systemd:
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<filename>bluetoothd.service</filename> might get activated either
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when Bluetooth hardware is plugged in, or when an application
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accesses its programming interfaces via D-Bus. Or, a print server
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daemon might 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 in the
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printer spool directory. Even for services that are intended to be
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started on system bootup unconditionally, it is a good idea to
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implement some of the various activation schemes outlined below,
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in order to maximize parallelization. If a daemon implements a
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D-Bus service or listening socket, implementing the full bus and
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socket activation scheme allows starting of the daemon with its
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clients in parallel (which speeds up boot-up), since all its
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communication channels are established already, and no request is
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lost because client requests will be queued by the bus system (in
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case of D-Bus) or the kernel (in case of sockets) until the
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activation is 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 exclusively on
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boot (and manually by the administrator) via SysV init scripts,
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as detailed in the <ulink
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url="http://refspecs.linuxbase.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
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Linux Standard Base Core Specification</ulink>. This method of
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activation is supported ubiquitously on Linux init systems, both
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old-style and new-style systems. Among other issues, SysV init
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scripts have the disadvantage of involving shell scripts in the
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boot process. New-style init systems generally employ updated
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versions of activation, both during boot-up and during runtime
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and using more minimal service description files.</para>
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<para>In systemd, if the developer or administrator wants to
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make sure that a service or other unit is activated
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automatically on boot, it is recommended to place a symlink to
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the unit file in the <filename>.wants/</filename> directory of
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either <filename>multi-user.target</filename> or
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<filename>graphical.target</filename>, which are normally used
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as boot targets at system startup. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details about the <filename>.wants/</filename> directories,
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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 parallelization and
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robustness and simplify configuration and development, it is
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recommended for all new-style daemons that communicate via
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listening sockets to employ socket-based activation. In a
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socket-based activation scheme, the creation and binding of the
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listening socket as primary communication channel of daemons to
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local (and sometimes remote) clients is moved out of the daemon
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code and into the init system. Based on per-daemon
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configuration, the init system installs the sockets and then
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hands them off to the spawned process as soon as the respective
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daemon is to be started. Optionally, activation of the service
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can be delayed until the first inbound traffic arrives at the
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socket to implement on-demand activation of daemons. However,
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the primary advantage of this scheme is that all providers and
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all consumers of the sockets can be started in parallel as soon
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as all sockets are established. In addition to that, daemons can
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be restarted with losing only a minimal number of client
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transactions, or even any client request at all (the latter is
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particularly true for state-less protocols, such as DNS or
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syslog), because the socket stays bound and accessible during
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the restart, and all requests are queued while the daemon cannot
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process them.</para>
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<para>New-style daemons which support socket activation must be
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able to receive their sockets from the init system instead of
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creating and binding them themselves. For details about the
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programming interfaces for 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>3</manvolnum></citerefentry>.
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For details about porting existing daemons to socket-based
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activation, see below. With minimal effort, it is possible to
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implement socket-based activation in addition to traditional
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internal socket creation in the same codebase in order to
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support both new-style and old-style init systems from the same
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daemon binary.</para>
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<para>systemd implements socket-based activation via
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<filename>.socket</filename> units, which are described in
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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When configuring socket units for socket-based activation, it is
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essential that all listening sockets are pulled in by the
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special target unit <filename>sockets.target</filename>. It is
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recommended to place a
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<varname>WantedBy=sockets.target</varname> directive in the
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[Install] section to automatically add such a
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dependency on installation of a socket unit. Unless
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<varname>DefaultDependencies=no</varname> is set, the necessary
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ordering dependencies are implicitly created for all socket
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units. For 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>.
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It is not necessary or recommended to place any additional
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dependencies on socket units (for example from
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<filename>multi-user.target</filename> or suchlike) when one is
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installed in <filename>sockets.target</filename>.</para>
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</refsect2>
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<refsect2>
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<title>Bus-Based Activation</title>
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<para>When the D-Bus IPC system is used for communication with
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clients, new-style daemons should employ bus activation so that
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they are automatically activated when a client application
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accesses their IPC interfaces. This is configured in D-Bus
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service files (not to be confused with systemd service unit
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files!). To ensure that D-Bus uses systemd to start-up and
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maintain the daemon, use the <varname>SystemdService=</varname>
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directive in these service files to configure the matching
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systemd service for a D-Bus service. e.g.: For a D-Bus service
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whose D-Bus activation file is named
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<filename>org.freedesktop.RealtimeKit.service</filename>, make
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sure to set
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<varname>SystemdService=rtkit-daemon.service</varname> in that
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file to bind it to the systemd service
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<filename>rtkit-daemon.service</filename>. This is needed to
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make sure that the daemon is started in a race-free fashion when
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activated via multiple mechanisms simultaneously.</para>
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</refsect2>
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<refsect2>
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<title>Device-Based Activation</title>
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<para>Often, daemons that manage a particular type of hardware
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should be activated only when the hardware of the respective
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kind is plugged in or otherwise becomes available. In a
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new-style init system, it is possible to bind activation to
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hardware plug/unplug events. In systemd, kernel devices
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appearing in the sysfs/udev device tree can be exposed as units
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if they are tagged with the string <literal>systemd</literal>.
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Like any other kind of unit, they may then pull in other units
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when activated (i.e. plugged in) and thus implement device-based
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activation. systemd dependencies may be encoded in the udev
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database via the <varname>SYSTEMD_WANTS=</varname> property. See
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<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. Often, it is nicer to pull in services from devices
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only indirectly via dedicated targets. Example: Instead of
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pulling in <filename>bluetoothd.service</filename> from all the
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various bluetooth dongles and other hardware available, pull in
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bluetooth.target from them and
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<filename>bluetoothd.service</filename> from that target. This
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provides for nicer abstraction and gives administrators the
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option to enable <filename>bluetoothd.service</filename> via
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controlling a <filename>bluetooth.target.wants/</filename>
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symlink uniformly with a command like <command>enable</command>
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of
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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instead of manipulating the udev ruleset.</para>
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</refsect2>
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<refsect2>
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<title>Path-Based Activation</title>
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<para>Often, runtime of daemons processing spool files or
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directories (such as a printing system) can be delayed until
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these file system objects change state, or become non-empty.
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New-style init systems provide a way to bind service activation
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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, there are
|
|
often 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
|
|
<constant>IP_FREEBIND</constant>/<constant>IPV6_FREEBIND</constant> 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 I/O 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 I/O schedulers. If a process executed by the init system shall not negatively impact the
|
|
amount of CPU or I/O 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
|
|
[Install] 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)
|
|
or <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 project='die-net'><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=auto])
|
|
AS_IF([test "x$with_systemdsystemunitdir" = "xyes" -o "x$with_systemdsystemunitdir" = "xauto"], [
|
|
def_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)
|
|
|
|
AS_IF([test "x$def_systemdsystemunitdir" = "x"],
|
|
[AS_IF([test "x$with_systemdsystemunitdir" = "xyes"],
|
|
[AC_MSG_ERROR([systemd support requested but pkg-config unable to query systemd package])])
|
|
with_systemdsystemunitdir=no],
|
|
[with_systemdsystemunitdir="$def_systemdsystemunitdir"])])
|
|
AS_IF([test "x$with_systemdsystemunitdir" != "xno"],
|
|
[AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])])
|
|
AM_CONDITIONAL([HAVE_SYSTEMD], [test "x$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 project='die-net'><refentrytitle>automake</refentrytitle><manvolnum>1</manvolnum></citerefentry>-based
|
|
projects:</para>
|
|
|
|
<programlisting>AM_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 project='die-net'><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
|
|
<constant>AF_UNIX</constant> 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 <constant>AF_UNIX</constant> 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>Placing Daemon Data</title>
|
|
|
|
<para>It is recommended to follow the general guidelines for
|
|
placing package files, as discussed in
|
|
<citerefentry><refentrytitle>file-hierarchy</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</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>,
|
|
<citerefentry><refentrytitle>file-hierarchy</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|