mirror of
https://github.com/systemd/systemd
synced 2024-09-15 22:30:22 +00:00
b040723ea4
This is a recurring submission and includes corrections to: comma placement.
204 lines
10 KiB
XML
204 lines
10 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">
|
||
|
||
<!--
|
||
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="sd_listen_fds">
|
||
|
||
<refentryinfo>
|
||
<title>sd_listen_fds</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>sd_listen_fds</refentrytitle>
|
||
<manvolnum>3</manvolnum>
|
||
</refmeta>
|
||
|
||
<refnamediv>
|
||
<refname>sd_listen_fds</refname>
|
||
<refname>SD_LISTEN_FDS_START</refname>
|
||
<refpurpose>Check for file descriptors passed by the system manager</refpurpose>
|
||
</refnamediv>
|
||
|
||
<refsynopsisdiv>
|
||
<funcsynopsis>
|
||
<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
|
||
|
||
<funcsynopsisinfo>#define SD_LISTEN_FDS_START 3</funcsynopsisinfo>
|
||
|
||
<funcprototype>
|
||
<funcdef>int <function>sd_listen_fds</function></funcdef>
|
||
<paramdef>int <parameter>unset_environment</parameter></paramdef>
|
||
</funcprototype>
|
||
</funcsynopsis>
|
||
</refsynopsisdiv>
|
||
|
||
<refsect1>
|
||
<title>Description</title>
|
||
|
||
<para><function>sd_listen_fds()</function> shall be
|
||
called by a daemon to check for file descriptors
|
||
passed by the init system as part of the socket-based
|
||
activation logic.</para>
|
||
|
||
<para>If the <parameter>unset_environment</parameter>
|
||
parameter is non-zero,
|
||
<function>sd_listen_fds()</function> will unset the
|
||
<varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname>
|
||
environment variables before returning (regardless of
|
||
whether the function call itself succeeded or
|
||
not). Further calls to
|
||
<function>sd_listen_fds()</function> will then fail,
|
||
but the variables are no longer inherited by child
|
||
processes.</para>
|
||
|
||
<para>If a daemon receives more than one file
|
||
descriptor, they will be passed in the same order as
|
||
configured in the systemd socket definition
|
||
file. Nonetheless, it is recommended to verify the
|
||
correct socket types before using them. To simplify
|
||
this checking, the functions
|
||
<citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
||
are provided. In order to maximize flexibility, it is
|
||
recommended to make these checks as loose as possible
|
||
without allowing incorrect setups. i.e. often, the
|
||
actual port number a socket is bound to matters little
|
||
for the service to work, hence it should not be
|
||
verified. On the other hand, whether a socket is a
|
||
datagram or stream socket matters a lot for the most
|
||
common program logics and should be checked.</para>
|
||
|
||
<para>This function call will set the FD_CLOEXEC flag
|
||
for all passed file descriptors to avoid further
|
||
inheritance to children of the calling process.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Return Value</title>
|
||
|
||
<para>On failure, this call returns a negative
|
||
errno-style error code. If
|
||
<varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname>
|
||
was not set or was not correctly set for this daemon and
|
||
hence no file descriptors were received, 0 is
|
||
returned. Otherwise, the number of file descriptors
|
||
passed is returned. The application may find them
|
||
starting with file descriptor SD_LISTEN_FDS_START,
|
||
i.e. file descriptor 3.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Notes</title>
|
||
|
||
<para>This function is provided by the reference
|
||
implementation of APIs for new-style daemons and
|
||
distributed with the systemd package. The algorithm it
|
||
implements is simple, and can easily be reimplemented
|
||
in daemons if it is important to support this
|
||
interface without using the reference
|
||
implementation.</para>
|
||
|
||
<para>Internally, this function checks whether the
|
||
<varname>$LISTEN_PID</varname> environment variable
|
||
equals the daemon PID. If not, it returns
|
||
immediately. Otherwise, it parses the number passed in
|
||
the <varname>$LISTEN_FDS</varname> environment
|
||
variable, then sets the FD_CLOEXEC flag for the parsed
|
||
number of file descriptors starting from
|
||
SD_LISTEN_FDS_START. Finally, it returns the parsed
|
||
number.</para>
|
||
|
||
<para>For details about the algorithm check the
|
||
liberally licensed reference implementation sources:
|
||
<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
|
||
and <ulink
|
||
url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
|
||
|
||
<para><function>sd_listen_fds()</function> is
|
||
implemented in the reference implementation's
|
||
<filename>sd-daemon.c</filename> and
|
||
<filename>sd-daemon.h</filename> files. These
|
||
interfaces are available as a shared library, which can
|
||
be compiled and linked to with the
|
||
<constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
||
file. Alternatively, applications consuming these APIs
|
||
may copy the implementation into their source
|
||
tree. For more details about the reference
|
||
implementation, see
|
||
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
|
||
|
||
<para>If the reference implementation is used as
|
||
drop-in files and -DDISABLE_SYSTEMD is set during
|
||
compilation, this function will always return 0 and
|
||
otherwise become a NOP.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Environment</title>
|
||
|
||
<variablelist class='environment-variables'>
|
||
<varlistentry>
|
||
<term><varname>$LISTEN_PID</varname></term>
|
||
<term><varname>$LISTEN_FDS</varname></term>
|
||
|
||
<listitem><para>Set by the init system
|
||
for supervised processes that use
|
||
socket-based activation. This
|
||
environment variable specifies the
|
||
data
|
||
<function>sd_listen_fds()</function>
|
||
parses. See above for
|
||
details.</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</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_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
||
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
||
</para>
|
||
</refsect1>
|
||
|
||
</refentry>
|