+ <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 || :
+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>
+
+ </refsect2>
~ianmdlvl / elogind.git / blobdiff