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<?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"
xmlns:xi="http://www.w3.org/2001/XInclude">
<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>$LISTEN_FDS</varname> and <varname>$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 unit file (see
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details). 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>
<para>If multiple socket units activate the same service the order
of the file descriptors passed to its main process is undefined.
If additional file descriptors have been passed to the service
manager using
<citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
<literal>FDSTORE=1</literal> messages, these file descriptors are
passed last, in arbitrary order, and with duplicates
removed.</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>
<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
<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>
</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>
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