Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- General Public License for more details.
+ Lesser General Public License for more details.
- You should have received a copy of the GNU General Public License
+ You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refnamediv>
<refname>daemon</refname>
- <refpurpose>Writing and Packaging System Daemons</refpurpose>
+ <refpurpose>Writing and packaging system daemons</refpurpose>
</refnamediv>
<refsect1>
<listitem><para>In the child, call
<function>fork()</function> again, to
- ensure the daemon can never re-aquire
+ ensure the daemon can never re-acquire
a terminal again.</para></listitem>
<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
- daemon process is reparented to
+ daemon process is re-parented to
init/PID 1, as all daemons should
be.</para></listitem>
<function>exit()</function> in the
original process. The process that
invoked the daemon must be able to
- rely that this
+ rely on that this
<function>exit()</function> happens
after initialization is complete and
all external communication channels
- established and
+ are established and
accessible.</para></listitem>
</orderedlist>
compatibility with SysV systems should
implement the scheme pointed out
above. However, it is recommended to make this
- behaviour optional and configurable via a
+ behavior optional and configurable via a
command line argument, to ease debugging as
well as to simplify integration into systems
using systemd.</para>
for details.</para></listitem>
<listitem><para>As much as possible,
- rely on the init systemd's
+ rely on the init system's
functionality to limit the access of
the daemon to files, services and
other resources. i.e. in the case of
<listitem><para>Instead of using the
<function>syslog()</function> call to log directly to the
- system logger, a new-style daemon may
+ system syslog service, a new-style daemon may
choose to simply log to STDERR via
<function>fprintf()</function>, which is then forwarded to
syslog by the init system. If log
<varname>StandardError=syslog</varname>
in the service unit file. For details
see
- <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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
+ activation is supported ubiquitously on Linux
init systems, both old-style and new-style
systems. Among other issues SysV init scripts
have the disadvantage of involving shell
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
+ started in parallel as soon as all sockets
are established. In addition to that daemons
can be restarted with losing only a minimal
number of client transactions or even any
<para>New-style daemons which support socket
activation must be able to receive their
- sockets from the init system, instead of of
+ sockets from the init system, instead 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
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>. For
details about porting existing daemons to
socket-based activation see below. With
minimal effort it is possible to implement
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
+ 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
<filename>bluetoothd.service</filename> via
controlling a
<filename>bluetooth.target.wants/</filename>
- symlink uniformly with a tool like
- <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ 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>
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
+ bandwidth available to other processes, it
should be configured with
<varname>CPUSchedulingPolicy=idle</varname>
and/or
<listitem><para>If your daemon
registers a D-Bus name on the bus,
make sure to use
- <varname>Type=dbus</varname> if
+ <varname>Type=dbus</varname> in the
+ service file if
possible.</para></listitem>
<listitem><para>Make sure to set a
system-independent.</para></listitem>
<listitem><para>Make sure to include
- an <literal>[Install]</literal> section including
- installation information for the unit
- file. See
+ 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.</para></listitem>
+ <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>
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
+ --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
- <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ 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>
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>
+if test "x$with_systemdsystemunitdir" != xno; then
+ AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])
+fi
+AM_CONDITIONAL(HAVE_SYSTEMD, [test -n "$with_systemdsystemunitdir" -a "x$with_systemdsystemunitdir" != xno ])</programlisting>
<para>This snippet allows automatic
installation of the unit files on systemd
machines, and optionally allows their
installation even on machines lacking
systemd. (Modification of this snippet for the
- session unit directory is left as excercise to the
+ user unit directory is left as an exercise for the
reader.)</para>
<para>Additionally, to ensure that
<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
+ <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>
+ 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
-/usr/bin/systemd-install --realize enable foobar.service foobar.socket >/dev/null 2>&1 || :
+%systemd_post foobar.service foobar.socket
%preun
-if [ "$1" -eq 0 ]; then
- /usr/bin/systemd-install --realize disable foobar.service foobar.socket >/dev/null 2>&1 || :
+%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>
<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
+ 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
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</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>,
~ianmdlvl / elogind.git / blobdiff