mirror of
https://github.com/systemd/systemd
synced 2024-09-06 16:56:43 +00:00
![Zbigniew Jędrzejewski-Szmek](/assets/img/avatar_default.png)
Files which are installed as-is (any .service and other unit files, .conf files, .policy files, etc), are left as is. My assumption is that SPDX identifiers are not yet that well known, so it's better to retain the extended header to avoid any doubt. I also kept any copyright lines. We can probably remove them, but it'd nice to obtain explicit acks from all involved authors before doing that.
247 lines
11 KiB
XML
247 lines
11 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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-->
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<refentry id="sd_listen_fds"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_listen_fds</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_listen_fds</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_listen_fds</refname>
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<refname>sd_listen_fds_with_names</refname>
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<refname>SD_LISTEN_FDS_START</refname>
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<refpurpose>Check for file descriptors passed by the system manager</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
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<funcsynopsisinfo>#define SD_LISTEN_FDS_START 3</funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_listen_fds</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_listen_fds_with_names</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>char*** <parameter>names</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_listen_fds()</function> may be invoked by a
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daemon to check for file descriptors passed by the service manager as
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part of the socket-based activation logic. It returns the number
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of received file descriptors. If no file descriptors have been
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received, zero is returned. The first file descriptor may be found
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at file descriptor number 3
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(i.e. <constant>SD_LISTEN_FDS_START</constant>), the remaining
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descriptors follow at 4, 5, 6, …, if any.</para>
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<para>If a daemon receives more than one file descriptor, they
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will be passed in the same order as configured in the systemd
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socket unit file (see
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details). Nonetheless, it is recommended to verify the correct
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socket types before using them. To simplify this checking, the
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functions
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<citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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are provided. In order to maximize flexibility, it is recommended
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to make these checks as loose as possible without allowing
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incorrect setups. i.e. often, the actual port number a socket is
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bound to matters little for the service to work, hence it should
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not be verified. On the other hand, whether a socket is a datagram
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or stream socket matters a lot for the most common program logics
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and should be checked.</para>
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<para>This function call will set the FD_CLOEXEC flag for all
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passed file descriptors to avoid further inheritance to children
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of the calling process.</para>
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<para>If multiple socket units activate the same service, the order
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of the file descriptors passed to its main process is undefined.
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If additional file descriptors have been passed to the service
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manager using
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<citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
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<literal>FDSTORE=1</literal> messages, these file descriptors are
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passed last, in arbitrary order, and with duplicates
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removed.</para>
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<para>If the <parameter>unset_environment</parameter> parameter is
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non-zero, <function>sd_listen_fds()</function> will unset the
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<varname>$LISTEN_FDS</varname>, <varname>$LISTEN_PID</varname> and
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<varname>$LISTEN_FDNAMES</varname> environment variables before
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returning (regardless of whether the function call itself
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succeeded or not). Further calls to
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<function>sd_listen_fds()</function> will then return zero, but the
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variables are no longer inherited by child processes.</para>
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<para><function>sd_listen_fds_with_names()</function> is like
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<function>sd_listen_fds()</function>, but optionally also returns
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an array of strings with identification names for the passed file
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descriptors, if that is available and the
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<parameter>names</parameter> parameter is non-NULL. This
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information is read from the <varname>$LISTEN_FDNAMES</varname>
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variable, which may contain a colon-separated list of names. For
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socket-activated services, these names may be configured with the
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<varname>FileDescriptorName=</varname> setting in socket unit
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files, see
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. For file descriptors pushed into the file descriptor
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store (see above), the name is set via the
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<varname>FDNAME=</varname> field transmitted via
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<function>sd_pid_notify_with_fds()</function>. The primary usecase
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for these names are services which accept a variety of file
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descriptors which are not recognizable with functions like
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<function>sd_is_socket()</function> alone, and thus require
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identification via a name. It is recommended to rely on named file
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descriptors only if identification via
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<function>sd_is_socket()</function> and related calls is not
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sufficient. Note that the names used are not unique in any
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way. The returned array of strings has as many entries as file
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descriptors have been received, plus a final NULL pointer
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terminating the array. The caller needs to free the array itself
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and each of its elements with libc's <function>free()</function>
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call after use. If the <parameter>names</parameter> parameter is
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NULL, the call is entirely equivalent to
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<function>sd_listen_fds()</function>.</para>
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<para>Under specific conditions, the following automatic file
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descriptor names are returned:
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<table>
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<title>
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<command>Special names</command>
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</title>
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<tgroup cols='2'>
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>unknown</literal></entry>
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<entry>The process received no name for the specific file descriptor from the service manager.</entry>
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</row>
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<row>
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<entry><literal>stored</literal></entry>
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<entry>The file descriptor originates in the service manager's per-service file descriptor store, and the <varname>FDNAME=</varname> field was absent when the file descriptor was submitted to the service manager.</entry>
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</row>
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<row>
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<entry><literal>connection</literal></entry>
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<entry>The service was activated in per-connection style using <varname>Accept=yes</varname> in the socket unit file, and the file descriptor is the connection socket.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On failure, these calls returns a negative errno-style error
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code. If
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<varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> was
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not set or was not correctly set for this daemon and hence no file
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descriptors were received, 0 is returned. Otherwise, the number of
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file descriptors passed is returned. The application may find them
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starting with file descriptor SD_LISTEN_FDS_START, i.e. file
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descriptor 3.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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<para>Internally, <function>sd_listen_fds()</function> checks
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whether the <varname>$LISTEN_PID</varname> environment variable
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equals the daemon PID. If not, it returns immediately. Otherwise,
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it parses the number passed in the <varname>$LISTEN_FDS</varname>
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environment variable, then sets the FD_CLOEXEC flag for the parsed
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number of file descriptors starting from SD_LISTEN_FDS_START.
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Finally, it returns the parsed
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number. <function>sd_listen_fds_with_names()</function> does the
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same but also parses <varname>$LISTEN_FDNAMES</varname> if
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set.</para>
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</refsect1>
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<refsect1>
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<title>Environment</title>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$LISTEN_PID</varname></term>
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<term><varname>$LISTEN_FDS</varname></term>
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<term><varname>$LISTEN_FDNAMES</varname></term>
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<listitem><para>Set by the service manager for supervised
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processes that use socket-based activation. This environment
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variable specifies the data
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<function>sd_listen_fds()</function> and
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<function>sd_listen_fds_with_names()</function> parses. See
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above for details.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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