mirror of
https://github.com/systemd/systemd.git
synced 2024-12-26 03:22:00 +03:00
681eb9cf2b
In particular, use /lib/systemd instead of /usr/lib/systemd in distributions like Debian which still have not adopted a /usr merge setup. Use XML entities from man/custom-entities.ent to replace configured paths while doing XSLT processing of the original XML files. There was precedent of some files (such as systemd.generator.xml) which were already using this approach. This addresses most of the (manual) fixes from this patch: http://anonscm.debian.org/cgit/pkg-systemd/systemd.git/tree/debian/patches/Fix-paths-in-man-pages.patch?h=experimental-220 The idea of using generic XML entities was presented here: http://lists.freedesktop.org/archives/systemd-devel/2015-May/032240.html This patch solves almost all the issues, with the exception of: - Path to /bin/mount and /bin/umount. - Generic statements about preference of /lib over /etc. These will be handled separately by follow up patches. Tested: - With default configure settings, ran "make install" to two separate directories and compared the output to confirm they matched exactly. - Used a set of configure flags including $CONFFLAGS from Debian: http://anonscm.debian.org/cgit/pkg-systemd/systemd.git/tree/debian/rules Installed the tree and confirmed the paths use /lib/systemd instead of /usr/lib/systemd and that no other unexpected differences exist. - Confirmed that `make distcheck` still passes.
769 lines
37 KiB
XML
769 lines
37 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
|
|
<!ENTITY % entities SYSTEM "custom-entities.ent" >
|
|
%entities;
|
|
]>
|
|
|
|
<!--
|
|
This file is part of systemd.
|
|
|
|
Copyright 2010 Lennart Poettering
|
|
|
|
systemd is free software; you can redistribute it and/or modify it
|
|
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
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public License
|
|
along with systemd; If not, see <http://www.gnu.org/licenses/>.
|
|
-->
|
|
|
|
<refentry id="daemon">
|
|
|
|
<refentryinfo>
|
|
<title>daemon</title>
|
|
<productname>systemd</productname>
|
|
|
|
<authorgroup>
|
|
<author>
|
|
<contrib>Developer</contrib>
|
|
<firstname>Lennart</firstname>
|
|
<surname>Poettering</surname>
|
|
<email>lennart@poettering.net</email>
|
|
</author>
|
|
</authorgroup>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>daemon</refentrytitle>
|
|
<manvolnum>7</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>daemon</refname>
|
|
<refpurpose>Writing and packaging system daemons</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para>A daemon is a service process that runs in the background
|
|
and supervises the system or provides functionality to other
|
|
processes. Traditionally, daemons are implemented following a
|
|
scheme originating in SysV Unix. Modern daemons should follow a
|
|
simpler yet more powerful scheme (here called "new-style"
|
|
daemons), as implemented by
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
|
|
This manual page covers both schemes, and in particular includes
|
|
recommendations for daemons that shall be included in the systemd
|
|
init system.</para>
|
|
|
|
<refsect2>
|
|
<title>SysV Daemons</title>
|
|
|
|
<para>When a traditional SysV daemon starts, it should execute
|
|
the following steps as part of the initialization. Note that
|
|
these steps are unnecessary for new-style daemons (see below),
|
|
and should only be implemented if compatibility with SysV is
|
|
essential.</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>Close all open file descriptors except
|
|
standard input, output, and error (i.e. the first three file
|
|
descriptors 0, 1, 2). This ensures that no accidentally passed
|
|
file descriptor stays around in the daemon process. On Linux,
|
|
this is best implemented by iterating through
|
|
<filename>/proc/self/fd</filename>, with a fallback of
|
|
iterating from file descriptor 3 to the value returned by
|
|
<function>getrlimit()</function> for
|
|
<constant>RLIMIT_NOFILE</constant>. </para></listitem>
|
|
|
|
<listitem><para>Reset all signal handlers to their default.
|
|
This is best done by iterating through the available signals
|
|
up to the limit of <constant>_NSIG</constant> and resetting
|
|
them to <constant>SIG_DFL</constant>.</para></listitem>
|
|
|
|
<listitem><para>Reset the signal mask
|
|
using
|
|
<function>sigprocmask()</function>.</para></listitem>
|
|
|
|
<listitem><para>Sanitize the environment block, removing or
|
|
resetting environment variables that might negatively impact
|
|
daemon runtime.</para></listitem>
|
|
|
|
<listitem><para>Call <function>fork()</function>, to create a
|
|
background process.</para></listitem>
|
|
|
|
<listitem><para>In the child, call
|
|
<function>setsid()</function> to detach from any terminal and
|
|
create an independent session.</para></listitem>
|
|
|
|
<listitem><para>In the child, call <function>fork()</function>
|
|
again, to 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 daemon process is
|
|
re-parented to init/PID 1, as all daemons should
|
|
be.</para></listitem>
|
|
|
|
<listitem><para>In the daemon process, connect
|
|
<filename>/dev/null</filename> to standard input, output, and
|
|
error.</para></listitem>
|
|
|
|
<listitem><para>In the daemon process, reset the umask to 0,
|
|
so that the file modes passed to <function>open()</function>,
|
|
<function>mkdir()</function> and suchlike directly control the
|
|
access mode of the created files and
|
|
directories.</para></listitem>
|
|
|
|
<listitem><para>In the daemon process, change the current
|
|
directory to the root directory (/), in order to avoid that
|
|
the daemon involuntarily blocks mount points from being
|
|
unmounted.</para></listitem>
|
|
|
|
<listitem><para>In the daemon process, write the daemon PID
|
|
(as returned by <function>getpid()</function>) to a PID file,
|
|
for example <filename>/run/foobar.pid</filename> (for a
|
|
hypothetical daemon "foobar") to ensure that the daemon cannot
|
|
be started more than once. This must be implemented in
|
|
race-free fashion so that the PID file is only updated when it
|
|
is verified at the same time that the PID previously stored in
|
|
the PID file no longer exists or belongs to a foreign
|
|
process.</para></listitem>
|
|
|
|
<listitem><para>In the daemon process, drop privileges, if
|
|
possible and applicable.</para></listitem>
|
|
|
|
<listitem><para>From the daemon process, notify the original
|
|
process started that initialization is complete. This can be
|
|
implemented via an unnamed pipe or similar communication
|
|
channel that is created before the first
|
|
<function>fork()</function> and hence available in both the
|
|
original and the daemon process.</para></listitem>
|
|
|
|
<listitem><para>Call <function>exit()</function> in the
|
|
original process. The process that invoked the daemon must be
|
|
able to rely on that this <function>exit()</function> happens
|
|
after initialization is complete and all external
|
|
communication channels are established and
|
|
accessible.</para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>The BSD <function>daemon()</function> function should not
|
|
be used, as it implements only a subset of these steps.</para>
|
|
|
|
<para>A daemon that needs to provide compatibility with SysV
|
|
systems should implement the scheme pointed out above. However,
|
|
it is recommended to make this behavior optional and
|
|
configurable via a command line argument to ease debugging as
|
|
well as to simplify integration into systems using
|
|
systemd.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>New-Style Daemons</title>
|
|
|
|
<para>Modern services for Linux should be implemented as
|
|
new-style daemons. This makes it easier to supervise and control
|
|
them at runtime and simplifies their implementation.</para>
|
|
|
|
<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 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 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 will be executed in their own
|
|
session, with standard input/output/error connected to
|
|
<filename>/dev/null</filename> unless otherwise configured. The
|
|
umask is reset.
|
|
</para>
|
|
|
|
<para>It is recommended for new-style daemons to implement the
|
|
following:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>If <constant>SIGTERM</constant> is received,
|
|
shut down the daemon and exit cleanly.</para></listitem>
|
|
|
|
<listitem><para>If <constant>SIGHUP</constant> is received,
|
|
reload the configuration files, if this
|
|
applies.</para></listitem>
|
|
|
|
<listitem><para>Provide a correct exit code from the main
|
|
daemon process, as this is used by the init system to detect
|
|
service errors and problems. It is recommended to follow the
|
|
exit code scheme as defined in the <ulink
|
|
url="http://refspecs.linuxbase.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB
|
|
recommendations for SysV init
|
|
scripts</ulink>.</para></listitem>
|
|
|
|
<listitem><para>If possible and applicable, expose the
|
|
daemon's control 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 your daemon
|
|
bus-activatable by supplying a D-Bus service activation
|
|
configuration file. This has multiple advantages: your daemon
|
|
may be started lazily on-demand; it may be started in parallel
|
|
to other daemons requiring it -- which maximizes
|
|
parallelization and boot-up speed; your daemon can be
|
|
restarted on failure without losing any bus requests, as the
|
|
bus queues requests for activatable services. See below for
|
|
details.</para></listitem>
|
|
|
|
<listitem><para>If your daemon provides services to other
|
|
local processes or remote clients via a socket, it should be
|
|
made socket-activatable following the scheme pointed out
|
|
below. Like D-Bus activation, this enables on-demand starting
|
|
of services as well as it allows improved parallelization of
|
|
service start-up. Also, for state-less 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>
|
|
|
|
<listitem><para>If applicable, a daemon should notify the init
|
|
system about startup completion or status updates via the
|
|
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
interface.</para></listitem>
|
|
|
|
<listitem><para>Instead of using the
|
|
<function>syslog()</function> call to log directly to the
|
|
system syslog service, a new-style daemon may choose to simply
|
|
log to standard error via <function>fprintf()</function>,
|
|
which is then forwarded to syslog by the init system. If log
|
|
levels are necessary, these can be encoded by prefixing
|
|
individual log lines with strings like
|
|
<literal><4></literal> (for log level 4 "WARNING" in the
|
|
syslog priority scheme), following a similar style as the
|
|
Linux kernel's <function>printk()</function> level system. For
|
|
details, see
|
|
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
and
|
|
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
|
|
|
|
</orderedlist>
|
|
|
|
<para>These recommendations are similar but not identical to the
|
|
<ulink
|
|
url="https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html">Apple
|
|
MacOS X Daemon Requirements</ulink>.</para>
|
|
</refsect2>
|
|
|
|
</refsect1>
|
|
<refsect1>
|
|
<title>Activation</title>
|
|
|
|
<para>New-style init systems provide multiple additional
|
|
mechanisms to activate services, as detailed below. It is common
|
|
that services are configured to be activated via more than one
|
|
mechanism at the same time. An example for systemd:
|
|
<filename>bluetoothd.service</filename> might get activated either
|
|
when Bluetooth hardware is plugged in, or when an application
|
|
accesses its programming interfaces via D-Bus. Or, a print server
|
|
daemon might get activated when traffic arrives at an IPP port, or
|
|
when a printer is plugged in, or when a file is queued in the
|
|
printer spool directory. Even for services that are intended to be
|
|
started on system bootup unconditionally, it is a good idea to
|
|
implement some of the various activation schemes outlined below,
|
|
in order to maximize parallelization. If a daemon implements a
|
|
D-Bus service or listening socket, implementing the full bus and
|
|
socket activation scheme allows starting of the daemon with its
|
|
clients in parallel (which speeds up boot-up), since all its
|
|
communication channels are established already, and no request is
|
|
lost because client requests will be queued by the bus system (in
|
|
case of D-Bus) or the kernel (in case of sockets) until the
|
|
activation is completed.</para>
|
|
|
|
<refsect2>
|
|
<title>Activation on Boot</title>
|
|
|
|
<para>Old-style daemons are usually activated exclusively on
|
|
boot (and manually by the administrator) via SysV init scripts,
|
|
as detailed in the <ulink
|
|
url="http://refspecs.linuxbase.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 that 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>
|
|
|
|
<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>
|
|
|
|
<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>
|
|
|
|
<para>Often, runtime of daemons processing spool files or
|
|
directories (such as a printing system) can be delayed until
|
|
these file system objects change state, or become non-empty.
|
|
New-style init systems provide a way to bind service activation
|
|
to file system changes. systemd implements this scheme via
|
|
path-based activation configured in <filename>.path</filename>
|
|
units, as outlined in
|
|
<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Timer-Based Activation</title>
|
|
|
|
<para>Some daemons that implement clean-up jobs that are
|
|
intended to be executed in regular intervals benefit from
|
|
timer-based activation. In systemd, this is implemented via
|
|
<filename>.timer</filename> units, as described in
|
|
<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Other Forms of Activation</title>
|
|
|
|
<para>Other forms of activation have been suggested and
|
|
implemented in some systems. However, 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
|
|
<constant>IP_FREEBIND</constant> 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>
|
|
|
|
<para>When writing systemd unit files, it is recommended to
|
|
consider the following suggestions:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>If possible, do not use the
|
|
<varname>Type=forking</varname> setting in service files. But
|
|
if you do, make sure to set the PID file path using
|
|
<varname>PIDFile=</varname>. See
|
|
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details.</para></listitem>
|
|
|
|
<listitem><para>If your daemon registers a D-Bus name on the
|
|
bus, make sure to use <varname>Type=dbus</varname> in the
|
|
service file if possible.</para></listitem>
|
|
|
|
<listitem><para>Make sure to set a good human-readable
|
|
description string with
|
|
<varname>Description=</varname>.</para></listitem>
|
|
|
|
<listitem><para>Do not disable
|
|
<varname>DefaultDependencies=</varname>, unless you really
|
|
know what you do and your unit is involved in early boot or
|
|
late system shutdown.</para></listitem>
|
|
|
|
<listitem><para>Normally, little if any dependencies should
|
|
need to be defined explicitly. However, if you do configure
|
|
explicit dependencies, only refer to unit names listed on
|
|
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
or names introduced by your own package to keep the unit file
|
|
operating system-independent.</para></listitem>
|
|
|
|
<listitem><para>Make sure to include an
|
|
<literal>[Install]</literal> section including installation
|
|
information for the unit file. See
|
|
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details. To activate your service on boot, make sure to
|
|
add a <varname>WantedBy=multi-user.target</varname> or
|
|
<varname>WantedBy=graphical.target</varname> directive. To
|
|
activate your socket on boot, make sure to add
|
|
<varname>WantedBy=sockets.target</varname>. Usually, you also
|
|
want to make sure that when your service is installed, your
|
|
socket is installed too, hence add
|
|
<varname>Also=foo.socket</varname> in your service file
|
|
<filename>foo.service</filename>, for a hypothetical program
|
|
<filename>foo</filename>.</para></listitem>
|
|
|
|
</orderedlist>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Installing Systemd Service Files</title>
|
|
|
|
<para>At the build installation time (e.g. <command>make
|
|
install</command> during package build), packages are
|
|
recommended to install their systemd unit files in the directory
|
|
returned by <command>pkg-config systemd
|
|
--variable=systemdsystemunitdir</command> (for system services)
|
|
or <command>pkg-config systemd
|
|
--variable=systemduserunitdir</command> (for user services).
|
|
This will make the services available in the system on explicit
|
|
request but not activate them automatically during boot.
|
|
Optionally, during package installation (e.g. <command>rpm
|
|
-i</command> by the administrator), symlinks should be created
|
|
in the systemd configuration directories via the
|
|
<command>enable</command> command of the
|
|
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
tool to activate them automatically on boot.</para>
|
|
|
|
<para>Packages using
|
|
<citerefentry project='die-net'><refentrytitle>autoconf</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
are recommended to use a configure script
|
|
excerpt like the following to determine the
|
|
unit installation path during source
|
|
configuration:</para>
|
|
|
|
<programlisting>PKG_PROG_PKG_CONFIG
|
|
AC_ARG_WITH([systemdsystemunitdir],
|
|
[AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [Directory for systemd service files])],,
|
|
[with_systemdsystemunitdir=auto])
|
|
AS_IF([test "x$with_systemdsystemunitdir" = "xyes" -o "x$with_systemdsystemunitdir" = "xauto"], [
|
|
def_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)
|
|
|
|
AS_IF([test "x$def_systemdsystemunitdir" = "x"],
|
|
[AS_IF([test "x$with_systemdsystemunitdir" = "xyes"],
|
|
[AC_MSG_ERROR([systemd support requested but pkg-config unable to query systemd package])])
|
|
with_systemdsystemunitdir=no],
|
|
[with_systemdsystemunitdir="$def_systemdsystemunitdir"])])
|
|
AS_IF([test "x$with_systemdsystemunitdir" != "xno"],
|
|
[AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])])
|
|
AM_CONDITIONAL([HAVE_SYSTEMD], [test "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
|
|
user unit directory is left as an exercise for the
|
|
reader.)</para>
|
|
|
|
<para>Additionally, to ensure that
|
|
<command>make distcheck</command> continues to
|
|
work, it is recommended to add the following
|
|
to the top-level <filename>Makefile.am</filename>
|
|
file in
|
|
<citerefentry project='die-net'><refentrytitle>automake</refentrytitle><manvolnum>1</manvolnum></citerefentry>-based
|
|
projects:</para>
|
|
|
|
<programlisting>DISTCHECK_CONFIGURE_FLAGS = \
|
|
--with-systemdsystemunitdir=$$dc_install_base/$(systemdsystemunitdir)</programlisting>
|
|
|
|
<para>Finally, unit files should be installed in the system with an automake excerpt like the following:</para>
|
|
|
|
<programlisting>if HAVE_SYSTEMD
|
|
systemdsystemunit_DATA = \
|
|
foobar.socket \
|
|
foobar.service
|
|
endif</programlisting>
|
|
|
|
<para>In the
|
|
<citerefentry project='die-net'><refentrytitle>rpm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
|
|
<filename>.spec</filename> file, use snippets like the following
|
|
to enable/disable the service during
|
|
installation/deinstallation. This makes use of the RPM macros
|
|
shipped along systemd. Consult the packaging guidelines of your
|
|
distribution for details and the equivalent for other package
|
|
managers.</para>
|
|
|
|
<para>At the top of the file:</para>
|
|
|
|
<programlisting>BuildRequires: systemd
|
|
%{?systemd_requires}</programlisting>
|
|
|
|
<para>And as scriptlets, further down:</para>
|
|
|
|
<programlisting>%post
|
|
%systemd_post foobar.service foobar.socket
|
|
|
|
%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 < 0.47.11-1
|
|
if /sbin/chkconfig --level 5 foobar ; then
|
|
/bin/systemctl --no-reload enable foobar.service foobar.socket >/dev/null 2>&1 || :
|
|
fi</programlisting>
|
|
|
|
<para>Where 0.47.11-1 is the first package version that includes
|
|
the native unit file. This fragment will ensure that the first
|
|
time the unit file is installed, it will be enabled if and only
|
|
if the SysV init script is enabled, thus making sure that the
|
|
enable status is not changed. Note that
|
|
<command>chkconfig</command> is a command specific to Fedora
|
|
which can be used to check whether a SysV init script is
|
|
enabled. Other operating systems will have to use different
|
|
commands here.</para>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<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>Placing Daemon Data</title>
|
|
|
|
<para>It is recommended to follow the general guidelines for
|
|
placing package files, as discussed in
|
|
<citerefentry><refentrytitle>file-hierarchy</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>file-hierarchy</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|