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man: add missing parts to man pages
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Lennart Poettering
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478
man/daemon.xml
478
man/daemon.xml
@ -57,7 +57,10 @@
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in SysV Unix. Modern daemons should follow a simpler
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yet more powerful scheme (here called "new-style"
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daemons), as implemented by
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. </para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. This
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manual page covers both schemes, and in
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particular includes recommendations for daemons that
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shall be included in the systemd init system.</para>
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<refsect2>
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<title>SysV Daemons</title>
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@ -252,26 +255,35 @@
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recommendations for SysV init
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scripts</ulink>.</para></listitem>
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<listitem><para>As much as possible,
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rely on systemd's functionality to
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limit the access of the daemon to
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files, services and other
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resources. i.e. rely on systemd's
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resource limit control instead of
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implementing your own, rely on
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systemd's privilege dropping code
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instead of implementing it in the
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daemon, and similar. See
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the available
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controls.</para></listitem>
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<listitem><para>If possible and
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applicable expose the daemon's control
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interface via the D-Bus IPC system and
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grab a bus name as last step of
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initialization.</para></listitem>
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<listitem><para>For integration in
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systemd, provide a
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<filename>.service</filename> unit
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file that carries information about
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starting, stopping and otherwise
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maintaining the daemon. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details.</para></listitem>
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<listitem><para>As much as possible,
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rely on the init systemd's
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functionality to limit the access of
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the daemon to files, services and
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other resources. i.e. in the case of
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systemd, rely on systemd's resource
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limit control instead of implementing
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your own, rely on systemd's privilege
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dropping code instead of implementing
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it in the daemon, and similar. See
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the available
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controls.</para></listitem>
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<listitem><para>If D-Bus is used, make
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your daemon bus-activatable, via
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supplying a D-Bus service activation
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@ -345,18 +357,308 @@
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MacOS X Daemon Requirements</ulink>.</para>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Activation</title>
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<para>New-style init systems provide multiple
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additional mechanisms to activate services, as
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detailed below. It is common that services are
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configured to be activated via more than one mechanism
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at the same time. An example for systemd:
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<filename>bluetoothd.service</filename> might get
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activated either when Bluetooth hardware is plugged
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in, or when an application accesses its programming
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interfaces via D-Bus. Or, a print server daemon might
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get activated when traffic arrives at an IPP port, or
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when a printer is plugged in, or when a file is queued
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in the printer spool directory. Even for services that
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are intended to be started on system bootup
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unconditionally it is a good idea to implement some of
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the various activation schemes outlined below, in
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order to maximize parallelization: if a daemon
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implements a D-Bus service or listening socket,
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implementing the full bus and socket activation scheme
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allows starting of the daemon with its clients in
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parallel (which speeds up boot-up), since all its
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communication channels are established already, and no
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request is lost because client requests will be queued
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by the bus system (in case of D-Bus) or the kernel (in
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case of sockets), until the activation
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completed.</para>
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<refsect2>
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<title>Activation on Boot</title>
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<para>Old-style daemons are usually activated
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exclusively on boot (and manually by the
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administrator) via SysV init scripts, as
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detailed in the <ulink
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url="http://refspecs.freestandards.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
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Linux Standard Base Core
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Specification</ulink>. This method of
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activation is supported ubiquitiously on Linux
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init systems, both old-style and new-style
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systems. Among other issues SysV init scripts
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have the disadvantage of involving shell
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scripts in the boot process. New-style init
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systems generally employ updated versions of
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activation, both during boot-up and during
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runtime and using more minimal service
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description files.</para>
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<para>In systemd, if the developer or
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administrator wants to make sure a service or
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other unit is activated automatically on boot
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it is recommended to place a symlink to the
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unit file in the <filename>.wants/</filename>
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directory of either
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<filename>multi-user.target</filename> or
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<filename>graphical.target</filename>, which
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are normally used as boot targets at system
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startup. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details about the
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<filename>.wants/</filename> directories, and
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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for details about the two boot targets.</para>
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</refsect2>
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<refsect2>
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<title>Socket-Based Activation</title>
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<para>In order to maximize the possible
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parallelization and robustness and simplify
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configuration and development, it is
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recommended for all new-style daemons that
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communicate via listening sockets to employ
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socket-based activation. In a socket-based
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activation scheme the creation and binding of
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the listening socket as primary communication
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channel of daemons to local (and sometimes
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remote) clients is moved out of the daemon
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code and into the init system. Based on
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per-daemon configuration the init system
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installs the sockets and then hands them off
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to the spawned process as soon as the
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respective daemon is to be started.
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Optionally activation of the service can be
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delayed until the first inbound traffic
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arrives at the socket, to implement on-demand
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activation of daemons. However, the primary
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advantage of this scheme is that all providers
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and all consumers of the sockets can be
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started in parallel as soon als all sockets
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are established. In addition to that daemons
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can be restarted with losing only a minimal
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number of client transactions or even any
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client request at all (the latter is
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particularly true for state-less protocols,
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such as DNS or syslog), because the socket
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stays bound and accessible during the restart,
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and all requests are queued while the daemon
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cannot process them.</para>
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<para>New-style daemons which support socket
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activation must be able to receive their
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sockets from the init system, instead of of
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creating and binding them themselves. For
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details about the programming interfaces for
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this scheme provided by systemd see
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<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>. For
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details about porting existing daemons to
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socket-based activation see below. With
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minimal effort it is possible to implement
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socket-based activation in addition to
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traditional internal socket creation in the
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same codebase in order to support both
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new-style and old-style init systems from the
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same daemon binary.</para>
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<para>systemd implements socket-based
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activation via <filename>.socket</filename>
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units, which are described in
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>. When
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configuring socket units for socket-based
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activation it is essential that all listening
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sockets are pulled in by the special target
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unit <filename>sockets.target</filename>. It
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is recommended to place a
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<varname>WantedBy=sockets.target</varname>
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directive in the <literal>[Install]</literal>
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section, to automatically add such a
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dependency on installation of a socket
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unit. Unless
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<varname>DefaultDependencies=no</varname> is
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set the necessary ordering dependencies are
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implicitly created for all socket units. For
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more information about
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<filename>sockets.target</filename> see
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>. It
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is not necessary or recommended to place any
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additional dependencies on socket units (for
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example from
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<filename>multi-user.target</filename> or
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suchlike) when one is installed in
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<filename>sockets.target</filename>.</para>
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</refsect2>
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<refsect2>
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<title>Bus-Based Activation</title>
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<para>When the D-Bus IPC system is used for
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communication with clients, new-style daemons
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should employ bus activation so that they are
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automatically activated when a client
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application accesses their IPC
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interfaces. This is configured in D-Bus
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service files (not to be confused with systemd
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service unit files!). To ensure that D-Bus
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uses systemd to start-up and maintain the
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daemon use the
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<varname>SystemdService=</varname> directive
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in these service files, to configure the
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matching systemd service for a D-Bus
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service. e.g.: for a D-Bus service whose D-Bus
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activation file is named
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<filename>org.freedesktop.RealtimeKit.service</filename>,
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make sure to set
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<varname>SystemdService=rtkit-daemon.service</varname>
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in that file, to bind it to the systemd
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service
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<filename>rtkit-daemon.service</filename>. This
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is needed to make sure that the daemon is
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started in a race-free fashion when activated
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via multiple mechanisms simultaneously.</para>
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</refsect2>
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<refsect2>
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<title>Device-Based Activation</title>
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<para>Often, daemons that manage a particular
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type of hardware should be activated only when
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the hardware of the respective kind is plugged
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in or otherwise becomes available. In a
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new-style init system it is possible to bind
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activation to hardware plug/unplug events. In systemd,
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kernel devices appearing in the sysfs/udev
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device tree can be exposed as units if they
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are tagged with the string
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"<literal>systemd</literal>". Like any other
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kind of unit they may then pull in other units
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when activated (i.e. Plugged in) and thus
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implement device-based activation. Systemd
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dependencies may be encoded in the udev
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database via the
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<varname>SYSTEMD_WANTS=</varname>
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property. See
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<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. Often it is nicer to pull in
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services from devices only indirectly via
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dedicated targets. Example: instead of pulling
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in <filename>bluetoothd.service</filename>
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from all the various bluetooth dongles and
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other hardware available, pull in
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bluetooth.target from them and
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<filename>bluetoothd.service</filename> from
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that target. This provides for nicer
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abstraction and gives administrators the
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option to enable
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<filename>bluetoothd.service</filename> via
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controlling a
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<filename>bluetooth.target.wants/</filename>
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symlink uniformly with a tool like
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<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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instead of manipulating the udev
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ruleset.</para>
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</refsect2>
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<refsect2>
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<title>Path-Based Activation</title>
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<para>Often, runtime of daemons processing
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spool files or directories (such as a printing
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system) can be delayed until these file system
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objects change state, or become
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non-empty. New-style init systems provide a
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way to bind service activation to file system
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changes. systemd implements this scheme via
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path-based activation configured in
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<filename>.path</filename> units, as outlined
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in
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<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
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</refsect2>
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<refsect2>
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<title>Timer-Based Activation</title>
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<para>Some daemons that implement clean-up
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jobs that are intended to be executed in
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regular intervals benefit from timer-based
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activation. In systemd, this is implemented
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via <filename>.timer</filename> units, as
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described in
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<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
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</refsect2>
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<refsect2>
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<title>Other Forms of Activation</title>
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<para>Other forms of activation have been
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suggested and implemented in some
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systems. However, often there are simpler or
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better alternatives, or they can be put
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together of combinations of the schemes
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above. Example: sometimes it appears useful to
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start daemons or <filename>.socket</filename>
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units when a specific IP address is configured
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on a network interface, because network
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sockets shall be bound to the
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address. However, an alternative to implement
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this is by utilizing the Linux IP_FREEBIND
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socket option, as accessible via
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<varname>FreeBind=yes</varname> in systemd
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socket files (see
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
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for details). This option, when enabled,
|
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allows sockets to be bound to a non-local, not
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configured IP address, and hence allows
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bindings to a particular IP address before it
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actually becomes available, making such an
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explicit dependency to the configured address
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redundant. Another often suggested trigger for
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service activation is low system
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load. However, here too, a more convincing
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approach might be to make proper use of
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features of the operating system: in
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particular, the CPU or IO scheduler of
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Linux. Instead of scheduling jobs from
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userspace based on monitoring the OS
|
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scheduler, it is advisable to leave the
|
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scheduling of processes to the OS scheduler
|
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itself. systemd provides fine-grained access
|
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to the CPU and IO schedulers. If a process
|
||||
executed by the init system shall not
|
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negatively impact the amount of CPU or IO
|
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bandwith available to other processes, it
|
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should be configured with
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<varname>CPUSchedulingPolicy=idle</varname>
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and/or
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<varname>IOSchedulingClass=idle</varname>. Optionally,
|
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this may be combined with timer-based
|
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activation to schedule background jobs during
|
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runtime and with minimal impact on the system,
|
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and remove it from the boot phase
|
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itself.</para>
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</refsect2>
|
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|
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</refsect1>
|
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<refsect1>
|
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<title>Integration with Systemd</title>
|
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|
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<refsect2>
|
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<title>Writing Systemd Unit Files</title>
|
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|
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@ -416,7 +718,7 @@
|
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</refsect2>
|
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|
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<refsect2>
|
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<title>Installing Service Files</title>
|
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<title>Installing Systemd Service Files</title>
|
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|
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<para>At the build installation time
|
||||
(e.g. <command>make install</command> during
|
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@ -488,7 +790,7 @@ endif</programlisting>
|
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during installation/deinstallation. Consult
|
||||
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>&1 || :
|
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@ -499,85 +801,70 @@ if [ "$1" -eq 0 ]; then
|
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fi</programlisting>
|
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|
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</refsect2>
|
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|
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<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>
|
||||
|
||||
<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>
|
||||
|
||||
</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 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 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 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>
|
||||
|
||||
<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>
|
||||
@ -587,7 +874,8 @@ fi</programlisting>
|
||||
<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>daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||||
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
||||
</para>
|
||||
</refsect1>
|
||||
|
||||
|
||||
@ -64,9 +64,11 @@
|
||||
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
||||
for the common options of all unit configuration
|
||||
files. The common configuration items are configured
|
||||
in the generic [Unit] and [Install] sections. A
|
||||
separate [Device] section does not exist, since no
|
||||
device-specific options may be configured.</para>
|
||||
in the generic <literal>[Unit]</literal> and
|
||||
<literal>[Install]</literal> sections. A separate
|
||||
<literal>[Device]</literal> section does not exist,
|
||||
since no device-specific options may be
|
||||
configured.</para>
|
||||
|
||||
<para>systemd will automatically create dynamic device
|
||||
units for all kernel devices that are marked with the
|
||||
@ -100,9 +102,15 @@
|
||||
<listitem><para>Adds dependencies of
|
||||
type <varname>Wants</varname> from
|
||||
this unit to all listed units. This
|
||||
may be used to activate arbitrary units,
|
||||
when a specific device becomes
|
||||
available.</para></listitem>
|
||||
may be used to activate arbitrary
|
||||
units, when a specific device becomes
|
||||
available. Note that this and the
|
||||
other tags are not taken into account
|
||||
unless the device is tagged with the
|
||||
"<literal>systemd</literal>" string in
|
||||
the udev database, because otherwise
|
||||
the device is not exposed as systemd
|
||||
unit.</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
|
||||
106
man/systemd.xml
106
man/systemd.xml
@ -196,6 +196,112 @@
|
||||
</variablelist>
|
||||
</refsect1>
|
||||
|
||||
<refsect1>
|
||||
<title>Concepts</title>
|
||||
|
||||
<para>systemd provides a dependency system between
|
||||
various entities called "units". Units encapsulate
|
||||
various objects that are relevant for system boot-up
|
||||
and maintainance. The majority of units are configured
|
||||
in unit configuration files, whose syntax and basic
|
||||
set of options is described in
|
||||
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
||||
however some are created automatically from other
|
||||
configuration or dynamically from system state. Units
|
||||
may be active (meaning started, bound, plugged in, ...
|
||||
depending on the unit type), or inactive (meaning
|
||||
stopped, unbound, unplugged, ...), as well is in the
|
||||
process of being activated or deactivated,
|
||||
i.e. between the two states. The following unit types
|
||||
are available:</para>
|
||||
|
||||
<orderedlist>
|
||||
<listitem><para>Service units, which control
|
||||
daemons and the processes they consist of. For
|
||||
details see
|
||||
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Socket units, which
|
||||
encapsulate local IPC or network sockets in
|
||||
the system, useful for socket-based
|
||||
activation. For details about socket units see
|
||||
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
||||
for details on socket-based activation and
|
||||
other forms of activation, see
|
||||
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Target units are useful to
|
||||
group units, or provide well-known
|
||||
synchronization points during boot-up, see
|
||||
<citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Device units expose kernel
|
||||
devices in systemd and may be used to
|
||||
implement device-based activation. For details
|
||||
see
|
||||
<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Mount units control mount
|
||||
points in the file system, for details see
|
||||
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Automount units provide
|
||||
automount capabilities, for on-demand mounting
|
||||
of file systems as well as parallelized
|
||||
boot-up. See
|
||||
<citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Snapshot units can be used to
|
||||
temporarily save the state of the set of
|
||||
systemd units, which later may be restored by
|
||||
activating the saved snapshot unit. For more
|
||||
information see
|
||||
<citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Timer units are useful for
|
||||
triggering activation of other units based on
|
||||
timers. You may find details in
|
||||
<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Swap units are very similar to
|
||||
mount units and encapsulated memory swap
|
||||
partitions or files of the operating
|
||||
systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
<listitem><para>Path units may be used
|
||||
activate other services when file system
|
||||
objects change or are modified. See
|
||||
<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
||||
|
||||
</orderedlist>
|
||||
|
||||
<para>Units are named as their configuration
|
||||
files. Some units have special semantics. A detailed
|
||||
list you may find in
|
||||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
|
||||
|
||||
<para>On boot systemd activates the target unit
|
||||
<filename>default.target</filename> whose job it is to
|
||||
activate on-boot services and other on-boot units by
|
||||
pulling them in via dependencies. Usually the unit
|
||||
name is just an alias (symlink) for either
|
||||
<filename>graphical.target</filename> (for
|
||||
fully-featured boots into the UI) or
|
||||
<filename>multi-user.target</filename> (for limited
|
||||
console-only boots for use in embedded or server
|
||||
environments, or similar; a subset of
|
||||
graphical.target). However it is at the discretion of
|
||||
the administrator to configure it as an alias to any
|
||||
other target unit. See
|
||||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
||||
for details about these target units.</para>
|
||||
|
||||
<para>For more information about the concepts and
|
||||
ideas behind systemd please refer to the <ulink
|
||||
url="http://0pointer.de/blog/projects/systemd.html">Original
|
||||
Announcement Document</ulink>.</para>
|
||||
</refsect1>
|
||||
|
||||
<refsect1>
|
||||
<title>Directories</title>
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user