namespace: include boot id in private tmp directories

[elogind.git] / man / daemon.xml

diff --git a/man/daemon.xml b/man/daemon.xml
index 853b3bb814790d6b3a35ad4c449b78ad7ee3e87f..7790420c6eb7154cfa80625f24fdb9db43cb0e2b 100644 (file)
--- a/man/daemon.xml
+++ b/man/daemon.xml
@@ -8,16 +8,16 @@
   Copyright 2010 Lennart Poettering
 
   systemd is free software; you can redistribute it and/or modify it
   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
   (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/>.
 -->
 
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 -->
 


@@ -44,7 +44,7 @@
 
         <refnamediv>
                 <refname>daemon</refname>
 
         <refnamediv>
                 <refname>daemon</refname>

-                <refpurpose>Writing and Packaging System Daemons</refpurpose>
+                <refpurpose>Writing and packaging system daemons</refpurpose>

         </refnamediv>
 
         <refsect1>
         </refnamediv>
 
         <refsect1>


@@ -57,7 +57,10 @@
                 in SysV Unix. Modern daemons should follow a simpler
                 yet more powerful scheme (here called "new-style"
                 daemons), as implemented by
                 in SysV Unix. Modern daemons should follow a simpler
                 yet more powerful scheme (here called "new-style"
                 daemons), as implemented by

-                <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. </para>
+                <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>
 
                 <refsect2>
                         <title>SysV Daemons</title>


@@ -76,7 +79,7 @@
                                 descriptors 0, 1, 2). This ensures
                                 that no accidentally passed file
                                 descriptor stays around in the daemon
                                 descriptors 0, 1, 2). This ensures
                                 that no accidentally passed file
                                 descriptor stays around in the daemon

-                                process. On Linux this is best
+                                process. On Linux, this is best

                                 implemented by iterating through
                                 <filename>/proc/self/fd</filename>,
                                 with a fallback of iterating from file
                                 implemented by iterating through
                                 <filename>/proc/self/fd</filename>,
                                 with a fallback of iterating from file


@@ -89,7 +92,7 @@
                                 best done by iterating through the
                                 available signals up to the limit of
                                 _NSIG and resetting them to
                                 best done by iterating through the
                                 available signals up to the limit of
                                 _NSIG and resetting them to

-                                SIG_DFL.</para></listitem>
+                                <constant>SIG_DFL</constant>.</para></listitem>

 
                                 <listitem><para>Reset the signal mask
                                 using
 
                                 <listitem><para>Reset the signal mask
                                 using


@@ -112,14 +115,14 @@
 
                                 <listitem><para>In the child, call
                                 <function>fork()</function> again, to
 
                                 <listitem><para>In the child, call
                                 <function>fork()</function> again, to

-                                ensure the daemon can never re-aquire
+                                ensure that 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
                                 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>
 
                                 init/PID 1, as all daemons should
                                 be.</para></listitem>
 


@@ -147,15 +150,15 @@
                                 <function>getpid()</function>) to a
                                 PID file, for example
                                 <filename>/var/run/foobar.pid</filename>
                                 <function>getpid()</function>) to a
                                 PID file, for example
                                 <filename>/var/run/foobar.pid</filename>

-                                (for a hypothetical daemon "foobar"),
+                                (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
                                 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
+                                it is verified at the same time that

                                 the PID previously stored in the PID
                                 file no longer exists or belongs to a
                                 the PID previously stored in the PID
                                 file no longer exists or belongs to a

-                                foreign process. Commonly some kind of
+                                foreign process. Commonly, some kind of

                                 file locking is employed to implement
                                 this logic.</para></listitem>
 
                                 file locking is employed to implement
                                 this logic.</para></listitem>
 


@@ -164,7 +167,7 @@
                                 applicable.</para></listitem>
 
                                 <listitem><para>From the daemon
                                 applicable.</para></listitem>
 
                                 <listitem><para>From the daemon

-                                process notify the original process
+                                process, notify the original process

                                 started that initialization is
                                 complete. This can be implemented via
                                 an unnamed pipe or similar
                                 started that initialization is
                                 complete. This can be implemented via
                                 an unnamed pipe or similar


@@ -178,11 +181,11 @@
                                 <function>exit()</function> in the
                                 original process. The process that
                                 invoked the daemon must be able to
                                 <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
                                 <function>exit()</function> happens
                                 after initialization is complete and
                                 all external communication channels

-                                established and
+                                are established and

                                 accessible.</para></listitem>
                         </orderedlist>
 
                                 accessible.</para></listitem>
                         </orderedlist>
 


@@ -193,8 +196,8 @@
                         compatibility with SysV systems should
                         implement the scheme pointed out
                         above. However, it is recommended to make this
                         compatibility with SysV systems should
                         implement the scheme pointed out
                         above. However, it is recommended to make this

-                        behaviour optional and configurable via a
-                        command line argument, to ease debugging as
+                        behavior optional and configurable via a
+                        command line argument to ease debugging as

                         well as to simplify integration into systems
                         using systemd.</para>
                 </refsect2>
                         well as to simplify integration into systems
                         using systemd.</para>
                 </refsect2>


@@ -208,20 +211,20 @@
                         runtime and simplifies their
                         implementation.</para>
 
                         runtime and simplifies their
                         implementation.</para>
 

-                        <para>For developing a new-style daemon none
+                        <para>For developing a new-style daemon, none

                         of the initialization steps recommended for
                         SysV daemons need to be implemented. New-style
                         init systems such as systemd make all of them
                         redundant. Moreover, since some of these steps
                         interfere with process monitoring, file
                         descriptor passing and other functionality of
                         of the initialization steps recommended for
                         SysV daemons need to be implemented. New-style
                         init systems such as systemd make all of them
                         redundant. Moreover, since some of these steps
                         interfere with process monitoring, file
                         descriptor passing and other functionality of

-                        the init system it is recommended not to
+                        the init system, it is recommended not to

                         execute them when run as new-style
                         service.</para>
 
                         <para>Note that new-style init systems
                         guarantee execution of daemon processes in
                         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
+                        a clean process context: 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
                         the environment block is sanitized, that the
                         signal handlers and mask is reset and that no
                         left-over file descriptors are passed. Daemons


@@ -234,11 +237,11 @@
                         to implement the following:</para>
 
                         <orderedlist>
                         to implement the following:</para>
 
                         <orderedlist>

-                                <listitem><para>If SIGTERM is
+                                <listitem><para>If <constant>SIGTERM</constant> is

                                 received, shut down the daemon and
                                 exit cleanly.</para></listitem>
 
                                 received, shut down the daemon and
                                 exit cleanly.</para></listitem>
 

-                                <listitem><para>If SIGHUP is received,
+                                <listitem><para>If <constant>SIGHUP</constant> is received,

                                 reload the configuration files, if
                                 this applies.</para></listitem>
 
                                 reload the configuration files, if
                                 this applies.</para></listitem>
 


@@ -252,28 +255,37 @@
                                 recommendations for SysV init
                                 scripts</ulink>.</para></listitem>
 
                                 recommendations for SysV init
                                 scripts</ulink>.</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. See
-                                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
-                                for the available
-                                controls.</para></listitem>
-

                                 <listitem><para>If possible and
                                 <listitem><para>If possible and

-                                applicable expose the daemon's control
+                                applicable, expose the daemon's control

                                 interface via the D-Bus IPC system and
                                 grab a bus name as last step of
                                 initialization.</para></listitem>
 
                                 interface via the D-Bus IPC system and
                                 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 system'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
                                 <listitem><para>If D-Bus is used, make

-                                your daemon bus-activatable, via
+                                your daemon bus-activatable by

                                 supplying a D-Bus service activation
                                 configuration file. This has multiple
                                 advantages: your daemon may be started
                                 supplying a D-Bus service activation
                                 configuration file. This has multiple
                                 advantages: your daemon may be started


@@ -281,7 +293,7 @@
                                 parallel to other daemons requiring it
                                 -- which maximizes parallelization and
                                 boot-up speed; your daemon can be
                                 parallel to other daemons requiring it
                                 -- which maximizes parallelization and
                                 boot-up speed; your daemon can be

-                                restarted on failure, without losing
+                                restarted on failure without losing

                                 any bus requests, as the bus queues
                                 requests for activatable services. See
                                 below for details.</para></listitem>
                                 any bus requests, as the bus queues
                                 requests for activatable services. See
                                 below for details.</para></listitem>


@@ -292,17 +304,17 @@
                                 socket, it should be made
                                 socket-activatable following the
                                 scheme pointed out below. Like D-Bus
                                 socket, it should be made
                                 socket-activatable following the
                                 scheme pointed out below. Like D-Bus

-                                activation this enables on-demand
+                                activation, this enables on-demand

                                 starting of services as well as it
                                 allows improved parallelization of
                                 service start-up. Also, for state-less
                                 starting of services as well as it
                                 allows improved parallelization of
                                 service start-up. Also, for state-less

-                                protocols (such as syslog, DNS) a
+                                protocols (such as syslog, DNS), a

                                 daemon implementing socket-based
                                 activation can be restarted without
                                 losing a single request. See below for
                                 details.</para></listitem>
 
                                 daemon implementing socket-based
                                 activation can be restarted without
                                 losing a single request. See below for
                                 details.</para></listitem>
 

-                                <listitem><para>If applicable a daemon
+                                <listitem><para>If applicable, a daemon

                                 should notify the init system about
                                 startup completion or status updates
                                 via the
                                 should notify the init system about
                                 startup completion or status updates
                                 via the


@@ -311,11 +323,11 @@
 
                                 <listitem><para>Instead of using the
                                 <function>syslog()</function> call to log directly to the
 
                                 <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
                                 choose to simply log to STDERR via
                                 <function>fprintf()</function>, which is then forwarded to
                                 syslog by the init system. If log

-                                priorities are necessary these can be
+                                priorities are necessary, these can be

                                 encoded by prefixing individual log
                                 lines with strings like "&lt;4&gt;"
                                 (for log priority 4 "WARNING" in the
                                 encoded by prefixing individual log
                                 lines with strings like "&lt;4&gt;"
                                 (for log priority 4 "WARNING" in the


@@ -331,9 +343,9 @@
                                 kind of logging may be enabled by
                                 setting
                                 <varname>StandardError=syslog</varname>
                                 kind of logging may be enabled by
                                 setting
                                 <varname>StandardError=syslog</varname>

-                                in the service unit file. For details
+                                in the service unit file. For details,

                                 see
                                 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>
 
                                 and
                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 


@@ -345,18 +357,309 @@
                         MacOS X Daemon Requirements</ulink>.</para>
                 </refsect2>
 
                         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 ubiquitously 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>Socket-Based Activation</title>
                 <refsect2>
                         <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 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
+                        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
+                        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>3</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>Bus-Based Activation</title>
                 </refsect2>
 
                 <refsect2>
                         <title>Bus-Based Activation</title>

+
+                        <para>When the D-Bus IPC system is used for
+                        communication with clients, new-style daemons
+                        should employ bus activation so that they are
+                        automatically activated when a client
+                        application accesses their IPC
+                        interfaces. This is configured in D-Bus
+                        service files (not to be confused with systemd
+                        service unit files!). To ensure that D-Bus
+                        uses systemd to start-up and maintain the
+                        daemon, use the
+                        <varname>SystemdService=</varname> directive
+                        in these service files to configure the
+                        matching systemd service for a D-Bus
+                        service. e.g.: For a D-Bus service whose D-Bus
+                        activation file is named
+                        <filename>org.freedesktop.RealtimeKit.service</filename>,
+                        make sure to set
+                        <varname>SystemdService=rtkit-daemon.service</varname>
+                        in that file to bind it to the systemd
+                        service
+                        <filename>rtkit-daemon.service</filename>. This
+                        is needed to make sure that the daemon is
+                        started in a race-free fashion when activated
+                        via multiple mechanisms simultaneously.</para>
+                </refsect2>
+
+                <refsect2>
+                        <title>Device-Based Activation</title>
+
+                        <para>Often, daemons that manage a particular
+                        type of hardware should be activated only when
+                        the hardware of the respective kind is plugged
+                        in or otherwise becomes available. In a
+                        new-style init system, it is possible to bind
+                        activation to hardware plug/unplug events. In
+                        systemd, kernel devices appearing in the
+                        sysfs/udev device tree can be exposed as units
+                        if they are tagged with the string
+                        <literal>systemd</literal>. Like any other
+                        kind of unit, they may then pull in other units
+                        when activated (i.e. plugged in) and thus
+                        implement device-based activation. systemd
+                        dependencies may be encoded in the udev
+                        database via the
+                        <varname>SYSTEMD_WANTS=</varname>
+                        property. See
+                        <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                        for details. Often, it is nicer to pull in
+                        services from devices only indirectly via
+                        dedicated targets. Example: Instead of pulling
+                        in <filename>bluetoothd.service</filename>
+                        from all the various bluetooth dongles and
+                        other hardware available, pull in
+                        bluetooth.target from them and
+                        <filename>bluetoothd.service</filename> from
+                        that target. This provides for nicer
+                        abstraction and gives administrators the
+                        option to enable
+                        <filename>bluetoothd.service</filename> via
+                        controlling a
+                        <filename>bluetooth.target.wants/</filename>
+                        symlink uniformly with a command like
+                        <command>enable</command> of
+                        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+                        instead of manipulating the udev
+                        ruleset.</para>

                 </refsect2>
 
                 <refsect2>
                         <title>Path-Based Activation</title>
                 </refsect2>
 
                 <refsect2>
                         <title>Path-Based Activation</title>

+
+                        <para>Often, runtime of daemons processing
+                        spool files or directories (such as a printing
+                        system) can be delayed until these file system
+                        objects change state, or become
+                        non-empty. New-style init systems provide a
+                        way to bind service activation to file system
+                        changes. systemd implements this scheme via
+                        path-based activation configured in
+                        <filename>.path</filename> units, as outlined
+                        in
+                        <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
+                </refsect2>
+
+                <refsect2>
+                        <title>Timer-Based Activation</title>
+
+                        <para>Some daemons that implement clean-up
+                        jobs that are intended to be executed in
+                        regular intervals benefit from timer-based
+                        activation. In systemd, this is implemented
+                        via <filename>.timer</filename> units, as
+                        described in
+                        <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

                 </refsect2>
 
                 </refsect2>
 

+                <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 IP_FREEBIND
+                        socket option, as accessible via
+                        <varname>FreeBind=yes</varname> in systemd
+                        socket files (see
+                        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                        for details). This option, when enabled,
+                        allows sockets to be bound to a non-local, not
+                        configured IP address, and hence allows
+                        bindings to a particular IP address before it
+                        actually becomes available, making such an
+                        explicit dependency to the configured address
+                        redundant. Another often suggested trigger for
+                        service activation is low system
+                        load. However, here too, a more convincing
+                        approach might be to make proper use of
+                        features of the operating system, in
+                        particular, the CPU or IO scheduler of
+                        Linux. Instead of scheduling jobs from
+                        userspace based on monitoring the OS
+                        scheduler, it is advisable to leave the
+                        scheduling of processes to the OS scheduler
+                        itself. systemd provides fine-grained access
+                        to the CPU and IO schedulers. If a process
+                        executed by the init system shall not
+                        negatively impact the amount of CPU or IO
+                        bandwidth available to other processes, it
+                        should be configured with
+                        <varname>CPUSchedulingPolicy=idle</varname>
+                        and/or
+                        <varname>IOSchedulingClass=idle</varname>. Optionally,
+                        this may be combined with timer-based
+                        activation to schedule background jobs during
+                        runtime and with minimal impact on the system,
+                        and remove it from the boot phase
+                        itself.</para>
+                </refsect2>
+
+        </refsect1>
+        <refsect1>
+                <title>Integration with Systemd</title>
+

                 <refsect2>
                         <title>Writing Systemd Unit Files</title>
 
                 <refsect2>
                         <title>Writing Systemd Unit Files</title>
 


@@ -365,7 +668,7 @@
                         suggestions:</para>
 
                         <orderedlist>
                         suggestions:</para>
 
                         <orderedlist>

-                                <listitem><para>If possible do not use
+                                <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
                                 the <varname>Type=forking</varname>
                                 setting in service files. But if you
                                 do, make sure to set the PID file path


@@ -376,7 +679,8 @@
                                 <listitem><para>If your daemon
                                 registers a D-Bus name on the bus,
                                 make sure to use
                                 <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
                                 possible.</para></listitem>
 
                                 <listitem><para>Make sure to set a


@@ -402,42 +706,54 @@
                                 system-independent.</para></listitem>
 
                                 <listitem><para>Make sure to include
                                 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
                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                 for details. To activate your service

-                                on boot make sure to add a
+                                on boot, make sure to add a

                                 <varname>WantedBy=multi-user.target</varname>
                                 or
                                 <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>
 
                 <refsect2>
 
                         </orderedlist>
                 </refsect2>
 
                 <refsect2>

-                        <title>Installing Service Files</title>
+                        <title>Installing Systemd Service Files</title>

 
                         <para>At the build installation time
                         (e.g. <command>make install</command> during
 
                         <para>At the build installation time
                         (e.g. <command>make install</command> during

-                        package build) packages are recommended to
+                        package build), packages are recommended to

                         install their systemd unit files in the
                         directory returned by <command>pkg-config
                         systemd
                         install their systemd unit files in the
                         directory returned by <command>pkg-config
                         systemd

-                        --variable=systemdsystemnunitdir</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>
                         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
+                        by the administrator), symlinks should be

                         created in the systemd configuration
                         created in the systemd configuration

-                        directories via the
-                        <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-                        tool, to activate them automatically on
+                        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
                         boot.</para>
 
                         <para>Packages using


@@ -451,15 +767,17 @@
 AC_ARG_WITH([systemdsystemunitdir],
         AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [Directory for systemd service files]),
         [], [with_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)])
 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
 
                         <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
                         reader.)</para>
 
                         <para>Additionally, to ensure that


@@ -483,111 +801,148 @@ endif</programlisting>
 
                         <para>In the
                         <citerefentry><refentrytitle>rpm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 
                         <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
                         the packaging guidelines of your distribution
                         for details and the equivalent for other

-                        packaging managers:</para>
+                        package managers.</para>

 
 

-                        <programlisting>%post
-/usr/bin/systemd-install enable foobar.service foobar.socket >/dev/null 2>&amp;1 || :
+                        <para>At the top of the file:</para>

 
 

-%preun
-if [ "$1" -eq 0 ]; then
-        /usr/bin/systemd-install disable foobar.service foobar.socket >/dev/null 2>&amp;1 || :
-fi</programlisting>
+                        <programlisting>BuildRequires: systemd
+%{?systemd_requires}</programlisting>

 
 

-                </refsect2>
+                        <para>And as scriptlets, further down:</para>

 
 

-                <refsect2>
-                        <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 this offers additional
-                        functionality to the daemons as well as it
-                        simplifies 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 createn 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
-                                file descriptors 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>
+                        <programlisting>%post
+%systemd_post foobar.service foobar.socket

 
 

-                                <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>
+%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 &lt; 0.47.11-1
+if /sbin/chkconfig --level 5 foobar ; then
+        /bin/systemctl --no-reload enable foobar.service foobar.socket >/dev/null 2>&amp;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>
                 </refsect2>

-

         </refsect1>
 
         </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>See Also</title>
                 <para>
                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 
         <refsect1>
                 <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>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>daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>

                 </para>
         </refsect1>
 
                 </para>
         </refsect1>