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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | ||
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2010 Lennart Poettering | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
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11 | under the terms of the GNU Lesser General Public License as published by |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
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13 | (at your option) any later version. |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
5430f7f2 | 18 | Lesser General Public License for more details. |
f9378423 | 19 | |
5430f7f2 | 20 | You should have received a copy of the GNU Lesser General Public License |
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21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. |
22 | --> | |
23 | ||
24 | <refentry id="sd_listen_fds"> | |
25 | ||
26 | <refentryinfo> | |
27 | <title>sd_listen_fds</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Lennart</firstname> | |
34 | <surname>Poettering</surname> | |
35 | <email>lennart@poettering.net</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>sd_listen_fds</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_listen_fds</refname> | |
976c46f8 | 47 | <refname>SD_LISTEN_FDS_START</refname> |
34511ca7 | 48 | <refpurpose>Check for file descriptors passed by the system manager</refpurpose> |
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49 | </refnamediv> |
50 | ||
51 | <refsynopsisdiv> | |
52 | <funcsynopsis> | |
a822cbfa | 53 | <funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo> |
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54 | |
55 | <funcsynopsisinfo>#define SD_LISTEN_FDS_START 3</funcsynopsisinfo> | |
56 | ||
57 | <funcprototype> | |
58 | <funcdef>int <function>sd_listen_fds</function></funcdef> | |
59 | <paramdef>int <parameter>unset_environment</parameter></paramdef> | |
60 | </funcprototype> | |
61 | </funcsynopsis> | |
62 | </refsynopsisdiv> | |
63 | ||
64 | <refsect1> | |
65 | <title>Description</title> | |
66 | ||
67 | <para><function>sd_listen_fds()</function> shall be | |
68 | called by a daemon to check for file descriptors | |
69 | passed by the init system as part of the socket-based | |
70 | activation logic.</para> | |
71 | ||
72 | <para>If the <parameter>unset_environment</parameter> | |
79640424 | 73 | parameter is non-zero, |
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74 | <function>sd_listen_fds()</function> will unset the |
75 | <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> | |
494a6682 | 76 | environment variables before returning (regardless of |
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77 | whether the function call itself succeeded or |
78 | not). Further calls to | |
79 | <function>sd_listen_fds()</function> will then fail, | |
80 | but the variables are no longer inherited by child | |
81 | processes.</para> | |
82 | ||
83 | <para>If a daemon receives more than one file | |
84 | descriptor, they will be passed in the same order as | |
85 | configured in the systemd socket definition | |
79640424 | 86 | file. Nonetheless, it is recommended to verify the |
f9378423 | 87 | correct socket types before using them. To simplify |
79640424 | 88 | this checking, the functions |
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89 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
90 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
91 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
92 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
79640424 | 93 | are provided. In order to maximize flexibility, it is |
436c44a5 | 94 | recommended to make these checks as loose as possible |
79640424 | 95 | without allowing incorrect setups. i.e. often, the |
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96 | actual port number a socket is bound to matters little |
97 | for the service to work, hence it should not be | |
98 | verified. On the other hand, whether a socket is a | |
99 | datagram or stream socket matters a lot for the most | |
af62c704 | 100 | common program logics and should be checked.</para> |
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101 | |
102 | <para>This function call will set the FD_CLOEXEC flag | |
103 | for all passed file descriptors to avoid further | |
104 | inheritance to children of the calling process.</para> | |
105 | </refsect1> | |
106 | ||
107 | <refsect1> | |
108 | <title>Return Value</title> | |
109 | ||
110 | <para>On failure, this call returns a negative | |
111 | errno-style error code. If | |
112 | <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> | |
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113 | was not set or was not correctly set for this daemon and |
114 | hence no file descriptors were received, 0 is | |
79640424 | 115 | returned. Otherwise, the number of file descriptors |
af62c704 | 116 | passed is returned. The application may find them |
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117 | starting with file descriptor SD_LISTEN_FDS_START, |
118 | i.e. file descriptor 3.</para> | |
119 | </refsect1> | |
120 | ||
121 | <refsect1> | |
122 | <title>Notes</title> | |
123 | ||
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124 | <para>These APIs are implemented as a shared library, |
125 | which can be compiled and linked to with the | |
126 | <constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
127 | file.</para> | |
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128 | |
129 | <para>Internally, this function checks whether the | |
130 | <varname>$LISTEN_PID</varname> environment variable | |
131 | equals the daemon PID. If not, it returns | |
79640424 | 132 | immediately. Otherwise, it parses the number passed in |
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133 | the <varname>$LISTEN_FDS</varname> environment |
134 | variable, then sets the FD_CLOEXEC flag for the parsed | |
135 | number of file descriptors starting from | |
79640424 | 136 | SD_LISTEN_FDS_START. Finally, it returns the parsed |
f9378423 | 137 | number.</para> |
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138 | </refsect1> |
139 | ||
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140 | <refsect1> |
141 | <title>Environment</title> | |
142 | ||
ccc9a4f9 | 143 | <variablelist class='environment-variables'> |
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144 | <varlistentry> |
145 | <term><varname>$LISTEN_PID</varname></term> | |
146 | <term><varname>$LISTEN_FDS</varname></term> | |
147 | ||
148 | <listitem><para>Set by the init system | |
149 | for supervised processes that use | |
150 | socket-based activation. This | |
151 | environment variable specifies the | |
152 | data | |
153 | <function>sd_listen_fds()</function> | |
154 | parses. See above for | |
155 | details.</para></listitem> | |
156 | </varlistentry> | |
157 | </variablelist> | |
158 | </refsect1> | |
159 | ||
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160 | <refsect1> |
161 | <title>See Also</title> | |
162 | ||
163 | <para> | |
160cd5c9 | 164 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
cb07866b | 165 | <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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166 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
167 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
168 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
169 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
170 | <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
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171 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
172 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
173 | </para> | |
174 | </refsect1> | |
175 | ||
176 | </refentry> |