along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
-<refentry id="systemd.special">
+<refentry id="daemon">
<refentryinfo>
<title>daemon</title>
functionality to other processes. Traditionally,
daemons are implemented following a scheme originating
in SysV Unix. Modern daemons should follow a simpler
- yet more powerful scheme here called "new-style"
- daemons, as implemented by systemd. </para>
+ yet more powerful scheme (here called "new-style"
+ daemons), as implemented by
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. This
+ manual page covers both schemes, and in
+ particular includes recommendations for daemons that
+ shall be included in the systemd init system.</para>
<refsect2>
<title>SysV Daemons</title>
<para>When a traditional SysV daemon
starts, it should execute the following steps
as part of the initialization. Note that these
- steps are unnecessary for new-style daemons,
+ steps are unnecessary for new-style daemons (see below),
and should only be implemented if compatibility
with SysV is essential.</para>
<filename>/proc/self/fd</filename>,
with a fallback of iterating from file
descriptor 3 to the value returned by
- getrlimit() for
+ <function>getrlimit()</function> for
RLIMIT_NOFILE.</para></listitem>
<listitem><para>Reset all signal
SIG_DFL.</para></listitem>
<listitem><para>Reset the signal mask
- using sigprocmask().</para></listitem>
+ using
+ <function>sigprocmask()</function>.</para></listitem>
- <listitem><para>Call fork(),
+ <listitem><para>Sanitize the
+ environment block, removing or
+ resetting environment variables that
+ might negatively impact daemon
+ runtime.</para></listitem>
+
+ <listitem><para>Call <function>fork()</function>,
to create a background
process.</para></listitem>
<listitem><para>In the child, call
- setsid() to detach from any terminal
- and create an independent
- session.</para></listitem>
+ <function>setsid()</function> to
+ detach from any terminal and create an
+ independent session.</para></listitem>
<listitem><para>In the child, call
- fork() again, to ensure the daemon can
- never re-aquire a terminal
- again.</para></listitem>
+ <function>fork()</function> again, to
+ ensure the daemon can never re-aquire
+ a terminal again.</para></listitem>
- <listitem><para>Call exit() in the
+ <listitem><para>Call <function>exit()</function> in the
first child, so that only the second
child (the actual daemon process)
stays around. This ensures that the
<listitem><para>In the daemon process,
reset the umask to 0, so that the file
- modes passed to open(), mkdir() and
+ modes passed to <function>open()</function>, <function>mkdir()</function> and
suchlike directly control the access
mode of the created files and
directories.</para></listitem>
blocks mount points from being
unmounted.</para></listitem>
+ <listitem><para>In the daemon process,
+ write the daemon PID (as returned by
+ <function>getpid()</function>) to a
+ PID file, for example
+ <filename>/var/run/foobar.pid</filename>
+ (for a hypothetical daemon "foobar"),
+ to ensure that the daemon cannot be
+ started more than once. This must be
+ implemented in race-free fashion so
+ that the PID file is only updated when
+ at the same time it is verified that
+ the PID previously stored in the PID
+ file no longer exists or belongs to a
+ foreign process. Commonly some kind of
+ file locking is employed to implement
+ this logic.</para></listitem>
+
<listitem><para>In the daemon process,
drop privileges, if possible and
applicable.</para></listitem>
complete. This can be implemented via
an unnamed pipe or similar
communication channel that is created
- before the first fork() and available
- in both processes.</para></listitem>
+ before the first
+ <function>fork()</function> and hence
+ available in both the original and the
+ daemon process.</para></listitem>
- <listitem><para>Call exit() in the
+ <listitem><para>Call
+ <function>exit()</function> in the
original process. The process that
invoked the daemon must be able to
- rely that this exit() happens after
- initialization is complete and all
- external communication channels
+ rely that this
+ <function>exit()</function> happens
+ after initialization is complete and
+ all external communication channels
established and
accessible.</para></listitem>
</orderedlist>
- <para>The BSD daemon() function should not be
- used, as it does only a subset of these steps.</para>
+ <para>The BSD <function>daemon()</function> function should not be
+ used, as it implements only a subset of these steps.</para>
<para>A daemon that needs to provide
compatibility with SysV systems should
execute them when run as new-style
service.</para>
+ <para>Note that new-style init systems
+ guarantee execution of daemon processes in
+ clean process contexts: it is guaranteed that
+ the environment block is sanitized, that the
+ signal handlers and mask is reset and that no
+ left-over file descriptors are passed. Daemons
+ will be executed in their own session, and
+ STDIN/STDOUT/STDERR connected to
+ <filename>/dev/null</filename> unless
+ otherwise configured. The umask is reset.</para>
+
<para>It is recommended for new-style daemons
to implement the following:</para>
this is used by the init system to
detect service errors and problems. It
is recommended to follow the exit code
- scheme as defined in LSB
- recommendations for SysV init scripts
- (http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html).</para></listitem>
-
- <listitem><para>As much as possible,
- rely on systemd's functionality to
- limit the access of the daemon to
- files, services and other
- resources. i.e. rely on systemd's
- resource limit control instead of
- implementing your own, rely on
- systemd's privilege dropping code
- instead of implementing it in the
- daemon, and similar.</para></listitem>
+ scheme as defined in the <ulink
+ url="http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
+ recommendations for SysV init
+ scripts</ulink>.</para></listitem>
<listitem><para>If possible and
applicable expose the daemon's control
grab a bus name as last step of
initialization.</para></listitem>
+ <listitem><para>For integration in
+ systemd, provide a
+ <filename>.service</filename> unit
+ file that carries information about
+ starting, stopping and otherwise
+ maintaining the daemon. See
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para></listitem>
+
+ <listitem><para>As much as possible,
+ rely on the init systemd's
+ functionality to limit the access of
+ the daemon to files, services and
+ other resources. i.e. in the case of
+ systemd, rely on systemd's resource
+ limit control instead of implementing
+ your own, rely on systemd's privilege
+ dropping code instead of implementing
+ it in the daemon, and similar. See
+ <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for the available
+ controls.</para></listitem>
+
<listitem><para>If D-Bus is used, make
your daemon bus-activatable, via
supplying a D-Bus service activation
boot-up speed; your daemon can be
restarted on failure, without losing
any bus requests, as the bus queues
- requests for activatable
- services.</para></listitem>
+ requests for activatable services. See
+ below for details.</para></listitem>
<listitem><para>If your daemon
provides services to other local
protocols (such as syslog, DNS) a
daemon implementing socket-based
activation can be restarted without
- losing a single
- request.</para></listitem>
+ losing a single request. See below for
+ details.</para></listitem>
<listitem><para>If applicable a daemon
should notify the init system about
- startup completion or status
- updates via the sd_notify()
+ startup completion or status updates
+ via the
+ <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
interface.</para></listitem>
<listitem><para>Instead of using the
- syslog() call to log directly to the
+ <function>syslog()</function> call to log directly to the
system logger, a new-style daemon may
choose to simply log to STDERR via
- fprintf(), which is then forwarded to
+ <function>fprintf()</function>, which is then forwarded to
syslog by the init system. If log
priorities are necessary these can be
encoded by prefixing individual log
(for log priority 4 "WARNING" in the
syslog priority scheme), following a
similar style as the Linux kernel's
- printk() priority system. In fact, using
- this style of logging also enables the
- init system to optionally direct all
- application logging to the kernel log
- buffer (kmsg), as accessible via
- dmesg.</para></listitem>
+ <function>printk()</function> priority system. In fact,
+ using this style of logging also
+ enables the init system to optionally
+ direct all application logging to the
+ kernel log buffer (kmsg), as
+ accessible via
+ <citerefentry><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>. This
+ kind of logging may be enabled by
+ setting
+ <varname>StandardError=syslog</varname>
+ in the service unit file. For details
+ see
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ and
+ <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
</orderedlist>
+
+ <para>These recommendations are similar but
+ not identical to the <ulink
+ url="http://developer.apple.com/mac/library/documentation/MacOSX/Conceptual/BPSystemStartup/Articles/LaunchOnDemandDaemons.html#//apple_ref/doc/uid/TP40001762-104738">Apple
+ MacOS X Daemon Requirements</ulink>.</para>
+ </refsect2>
+
+ </refsect1>
+ <refsect1>
+ <title>Activation</title>
+
+ <para>New-style init systems provide multiple
+ additional mechanisms to activate services, as
+ detailed below. It is common that services are
+ configured to be activated via more than one mechanism
+ at the same time. An example for systemd:
+ <filename>bluetoothd.service</filename> might get
+ activated either when Bluetooth hardware is plugged
+ in, or when an application accesses its programming
+ interfaces via D-Bus. Or, a print server daemon might
+ get activated when traffic arrives at an IPP port, or
+ when a printer is plugged in, or when a file is queued
+ in the printer spool directory. Even for services that
+ are intended to be started on system bootup
+ unconditionally it is a good idea to implement some of
+ the various activation schemes outlined below, in
+ order to maximize parallelization: if a daemon
+ implements a D-Bus service or listening socket,
+ implementing the full bus and socket activation scheme
+ allows starting of the daemon with its clients in
+ parallel (which speeds up boot-up), since all its
+ communication channels are established already, and no
+ request is lost because client requests will be queued
+ by the bus system (in case of D-Bus) or the kernel (in
+ case of sockets), until the activation is
+ completed.</para>
+
+ <refsect2>
+ <title>Activation on Boot</title>
+
+ <para>Old-style daemons are usually activated
+ exclusively on boot (and manually by the
+ administrator) via SysV init scripts, as
+ detailed in the <ulink
+ url="http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
+ Linux Standard Base Core
+ Specification</ulink>. This method of
+ activation is supported ubiquitiously on Linux
+ init systems, both old-style and new-style
+ systems. Among other issues SysV init scripts
+ have the disadvantage of involving shell
+ scripts in the boot process. New-style init
+ systems generally employ updated versions of
+ activation, both during boot-up and during
+ runtime and using more minimal service
+ description files.</para>
+
+ <para>In systemd, if the developer or
+ administrator wants to make sure a service or
+ other unit is activated automatically on boot
+ it is recommended to place a symlink to the
+ unit file in the <filename>.wants/</filename>
+ directory of either
+ <filename>multi-user.target</filename> or
+ <filename>graphical.target</filename>, which
+ are normally used as boot targets at system
+ startup. See
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details about the
+ <filename>.wants/</filename> directories, and
+ <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ for details about the two boot targets.</para>
+
</refsect2>
<refsect2>
- <title>Bus Activation</title>
+ <title>Socket-Based Activation</title>
+
+ <para>In order to maximize the possible
+ parallelization and robustness and simplify
+ configuration and development, it is
+ recommended for all new-style daemons that
+ communicate via listening sockets to employ
+ socket-based activation. In a socket-based
+ activation scheme the creation and binding of
+ the listening socket as primary communication
+ channel of daemons to local (and sometimes
+ remote) clients is moved out of the daemon
+ code and into the init system. Based on
+ per-daemon configuration the init system
+ installs the sockets and then hands them off
+ to the spawned process as soon as the
+ respective daemon is to be started.
+ Optionally activation of the service can be
+ delayed until the first inbound traffic
+ arrives at the socket, to implement on-demand
+ activation of daemons. However, the primary
+ advantage of this scheme is that all providers
+ and all consumers of the sockets can be
+ started in parallel as soon als all sockets
+ are established. In addition to that daemons
+ can be restarted with losing only a minimal
+ number of client transactions or even any
+ client request at all (the latter is
+ particularly true for state-less protocols,
+ such as DNS or syslog), because the socket
+ stays bound and accessible during the restart,
+ and all requests are queued while the daemon
+ cannot process them.</para>
+
+ <para>New-style daemons which support socket
+ activation must be able to receive their
+ sockets from the init system, instead of of
+ creating and binding them themselves. For
+ details about the programming interfaces for
+ this scheme provided by systemd see
+ <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ and
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>. For
+ details about porting existing daemons to
+ socket-based activation see below. With
+ minimal effort it is possible to implement
+ socket-based activation in addition to
+ traditional internal socket creation in the
+ same codebase in order to support both
+ new-style and old-style init systems from the
+ same daemon binary.</para>
+
+ <para>systemd implements socket-based
+ activation via <filename>.socket</filename>
+ units, which are described in
+ <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>. When
+ configuring socket units for socket-based
+ activation it is essential that all listening
+ sockets are pulled in by the special target
+ unit <filename>sockets.target</filename>. It
+ is recommended to place a
+ <varname>WantedBy=sockets.target</varname>
+ directive in the <literal>[Install]</literal>
+ section, to automatically add such a
+ dependency on installation of a socket
+ unit. Unless
+ <varname>DefaultDependencies=no</varname> is
+ set the necessary ordering dependencies are
+ implicitly created for all socket units. For
+ more information about
+ <filename>sockets.target</filename> see
+ <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>. It
+ is not necessary or recommended to place any
+ additional dependencies on socket units (for
+ example from
+ <filename>multi-user.target</filename> or
+ suchlike) when one is installed in
+ <filename>sockets.target</filename>.</para>
</refsect2>
<refsect2>
- <title>Socket Activation</title>
+ <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>Writing Service Files</title>
+ <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>Installing Service Files</title>
+ <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
+ bandwith 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>Since not all syslog
+ implementations are socket-activatable
+ yet, it is recommended to place an
+ <varname>After=syslog.target</varname>
+ dependency in service files for
+ daemons that can log to
+ syslog. <filename>syslog.target</filename>
+ then either pulls in the syslog daemon
+ itself or simply the activation
+ socket. A <varname>Wants=</varname> or
+ even <varname>Requires=</varname>
+ dependency should generally not be
+ added, since it should be up to the
+ administrator whether he wants to
+ enable logging or not, and most syslog
+ clients work fine if no log daemon is
+ running.</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=systemdsessionunitdir</command>
+ (for session 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)])
+AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])
+AM_CONDITIONAL(HAVE_SYSTEMD, [test -n "$with_systemdsystemunitdir"])</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
+ session unit directory is left as excercise to 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 a snippet like
+ the following to enable/disable the service
+ during installation/deinstallation. Consult
+ the packaging guidelines of your distribution
+ for details and the equivalent for other
+ package managers:</para>
+
+ <programlisting>%post
+if [ $1 -eq 1 ]; then
+ # Enable (but don't start) the units by default
+ /bin/systemctl enable foobar.service foobar.socket >/dev/null 2>&1 || :
+
+ # Alternatively, just call /bin/systemctl daemon-reload here,
+ # if the daemon should not be enabled by default on package
+ # installation
+fi
+
+%preun
+if [ $1 -eq 0 ]; then
+ # Disable and stop the units
+ /bin/systemctl disable foobar.service foobar.socket >/dev/null 2>&1 || :
+ /bin/systemctl stop foobar.service foobar.socket >/dev/null 2>&1 || :
+fi
+
+%postun
+if [ $1 -ge 1 ] ; then
+ # On upgrade, reload init system configuration if we changed unit files
+ /bin/systemctl daemon-reload >/dev/null 2>&1 || :
+ # On upgrade, restart the daemon
+ /bin/systemctl try-restart foobar.service >/dev/null 2>&1 || :
+fi</programlisting>
+
+ <para>Depending on whether your service should
+ or should not be started/stopped/restarted
+ during package installation, deinstallation or
+ upgrade, a different set of commands may be
+ specified. See
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ for details.</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>%triggerin -- foobar < 0.47.11-1
+if /sbin/chkconfig foobar ; then
+ /bin/systemctl 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 the enable
+ status is not changed. Note that
+ <command>chkconfig</command> is a command
+ specific 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>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
</para>
</refsect1>
~ianmdlvl / elogind.git / blobdiff