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514094f9 | 1 | <?xml version='1.0'?> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
f9378423 | 5 | |
6a70f3aa | 6 | <refentry id="sd_listen_fds" |
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7 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
8 | ||
9 | <refentryinfo> | |
10 | <title>sd_listen_fds</title> | |
11 | <productname>systemd</productname> | |
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12 | </refentryinfo> |
13 | ||
14 | <refmeta> | |
15 | <refentrytitle>sd_listen_fds</refentrytitle> | |
16 | <manvolnum>3</manvolnum> | |
17 | </refmeta> | |
18 | ||
19 | <refnamediv> | |
20 | <refname>sd_listen_fds</refname> | |
8dd4c05b | 21 | <refname>sd_listen_fds_with_names</refname> |
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22 | <refname>SD_LISTEN_FDS_START</refname> |
23 | <refpurpose>Check for file descriptors passed by the system manager</refpurpose> | |
24 | </refnamediv> | |
25 | ||
26 | <refsynopsisdiv> | |
27 | <funcsynopsis> | |
28 | <funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo> | |
29 | ||
30 | <funcsynopsisinfo>#define SD_LISTEN_FDS_START 3</funcsynopsisinfo> | |
31 | ||
32 | <funcprototype> | |
33 | <funcdef>int <function>sd_listen_fds</function></funcdef> | |
34 | <paramdef>int <parameter>unset_environment</parameter></paramdef> | |
35 | </funcprototype> | |
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36 | |
37 | <funcprototype> | |
38 | <funcdef>int <function>sd_listen_fds_with_names</function></funcdef> | |
39 | <paramdef>int <parameter>unset_environment</parameter></paramdef> | |
40 | <paramdef>char*** <parameter>names</parameter></paramdef> | |
41 | </funcprototype> | |
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42 | </funcsynopsis> |
43 | </refsynopsisdiv> | |
44 | ||
45 | <refsect1> | |
46 | <title>Description</title> | |
47 | ||
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48 | <para><function>sd_listen_fds()</function> may be invoked by a |
49 | daemon to check for file descriptors passed by the service manager as | |
50 | part of the socket-based activation logic. It returns the number | |
51 | of received file descriptors. If no file descriptors have been | |
b938cb90 | 52 | received, zero is returned. The first file descriptor may be found |
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53 | at file descriptor number 3 |
54 | (i.e. <constant>SD_LISTEN_FDS_START</constant>), the remaining | |
1eecafb8 | 55 | descriptors follow at 4, 5, 6, …, if any.</para> |
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56 | |
57 | <para>If a daemon receives more than one file descriptor, they | |
58 | will be passed in the same order as configured in the systemd | |
59 | socket unit file (see | |
60 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
61 | for details). Nonetheless, it is recommended to verify the correct | |
62 | socket types before using them. To simplify this checking, the | |
63 | functions | |
64 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
65 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
66 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
67 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
68 | are provided. In order to maximize flexibility, it is recommended | |
69 | to make these checks as loose as possible without allowing | |
70 | incorrect setups. i.e. often, the actual port number a socket is | |
71 | bound to matters little for the service to work, hence it should | |
72 | not be verified. On the other hand, whether a socket is a datagram | |
73 | or stream socket matters a lot for the most common program logics | |
74 | and should be checked.</para> | |
75 | ||
76 | <para>This function call will set the FD_CLOEXEC flag for all | |
77 | passed file descriptors to avoid further inheritance to children | |
78 | of the calling process.</para> | |
79 | ||
b938cb90 | 80 | <para>If multiple socket units activate the same service, the order |
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81 | of the file descriptors passed to its main process is undefined. |
82 | If additional file descriptors have been passed to the service | |
83 | manager using | |
84 | <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s | |
85 | <literal>FDSTORE=1</literal> messages, these file descriptors are | |
86 | passed last, in arbitrary order, and with duplicates | |
87 | removed.</para> | |
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88 | |
89 | <para>If the <parameter>unset_environment</parameter> parameter is | |
90 | non-zero, <function>sd_listen_fds()</function> will unset the | |
91 | <varname>$LISTEN_FDS</varname>, <varname>$LISTEN_PID</varname> and | |
92 | <varname>$LISTEN_FDNAMES</varname> environment variables before | |
93 | returning (regardless of whether the function call itself | |
94 | succeeded or not). Further calls to | |
95 | <function>sd_listen_fds()</function> will then return zero, but the | |
96 | variables are no longer inherited by child processes.</para> | |
97 | ||
98 | <para><function>sd_listen_fds_with_names()</function> is like | |
b938cb90 | 99 | <function>sd_listen_fds()</function>, but optionally also returns |
8dd4c05b | 100 | an array of strings with identification names for the passed file |
b938cb90 | 101 | descriptors, if that is available and the |
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102 | <parameter>names</parameter> parameter is non-NULL. This |
103 | information is read from the <varname>$LISTEN_FDNAMES</varname> | |
104 | variable, which may contain a colon-separated list of names. For | |
105 | socket-activated services, these names may be configured with the | |
106 | <varname>FileDescriptorName=</varname> setting in socket unit | |
107 | files, see | |
108 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
109 | for details. For file descriptors pushed into the file descriptor | |
b938cb90 | 110 | store (see above), the name is set via the |
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111 | <varname>FDNAME=</varname> field transmitted via |
112 | <function>sd_pid_notify_with_fds()</function>. The primary usecase | |
113 | for these names are services which accept a variety of file | |
114 | descriptors which are not recognizable with functions like | |
115 | <function>sd_is_socket()</function> alone, and thus require | |
116 | identification via a name. It is recommended to rely on named file | |
117 | descriptors only if identification via | |
118 | <function>sd_is_socket()</function> and related calls is not | |
119 | sufficient. Note that the names used are not unique in any | |
120 | way. The returned array of strings has as many entries as file | |
a8eaaee7 | 121 | descriptors have been received, plus a final NULL pointer |
8dd4c05b | 122 | terminating the array. The caller needs to free the array itself |
ba6bfc0d | 123 | and each of its elements with libc's <function>free()</function> |
8dd4c05b | 124 | call after use. If the <parameter>names</parameter> parameter is |
b938cb90 | 125 | NULL, the call is entirely equivalent to |
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126 | <function>sd_listen_fds()</function>.</para> |
127 | ||
b938cb90 | 128 | <para>Under specific conditions, the following automatic file |
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129 | descriptor names are returned: |
130 | ||
131 | <table> | |
132 | <title> | |
133 | <command>Special names</command> | |
134 | </title> | |
135 | ||
136 | <tgroup cols='2'> | |
137 | <thead> | |
138 | <row> | |
139 | <entry>Name</entry> | |
140 | <entry>Description</entry> | |
141 | </row> | |
142 | </thead> | |
143 | <tbody> | |
144 | <row> | |
145 | <entry><literal>unknown</literal></entry> | |
146 | <entry>The process received no name for the specific file descriptor from the service manager.</entry> | |
147 | </row> | |
148 | ||
149 | <row> | |
150 | <entry><literal>stored</literal></entry> | |
151 | <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> | |
152 | </row> | |
153 | ||
154 | <row> | |
155 | <entry><literal>connection</literal></entry> | |
156 | <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> | |
157 | </row> | |
158 | </tbody> | |
159 | </tgroup> | |
160 | </table> | |
161 | </para> | |
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162 | </refsect1> |
163 | ||
164 | <refsect1> | |
165 | <title>Return Value</title> | |
166 | ||
8dd4c05b | 167 | <para>On failure, these calls returns a negative errno-style error |
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168 | code. If |
169 | <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> was | |
170 | not set or was not correctly set for this daemon and hence no file | |
171 | descriptors were received, 0 is returned. Otherwise, the number of | |
172 | file descriptors passed is returned. The application may find them | |
173 | starting with file descriptor SD_LISTEN_FDS_START, i.e. file | |
174 | descriptor 3.</para> | |
175 | </refsect1> | |
176 | ||
177 | <refsect1> | |
178 | <title>Notes</title> | |
179 | ||
180 | <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/> | |
181 | ||
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182 | <para>Internally, <function>sd_listen_fds()</function> checks |
183 | whether the <varname>$LISTEN_PID</varname> environment variable | |
184 | equals the daemon PID. If not, it returns immediately. Otherwise, | |
185 | it parses the number passed in the <varname>$LISTEN_FDS</varname> | |
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186 | environment variable, then sets the FD_CLOEXEC flag for the parsed |
187 | number of file descriptors starting from SD_LISTEN_FDS_START. | |
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188 | Finally, it returns the parsed |
189 | number. <function>sd_listen_fds_with_names()</function> does the | |
190 | same but also parses <varname>$LISTEN_FDNAMES</varname> if | |
191 | set.</para> | |
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192 | </refsect1> |
193 | ||
194 | <refsect1> | |
195 | <title>Environment</title> | |
196 | ||
197 | <variablelist class='environment-variables'> | |
198 | <varlistentry> | |
199 | <term><varname>$LISTEN_PID</varname></term> | |
200 | <term><varname>$LISTEN_FDS</varname></term> | |
8dd4c05b | 201 | <term><varname>$LISTEN_FDNAMES</varname></term> |
798d3a52 | 202 | |
8dd4c05b LP |
203 | <listitem><para>Set by the service manager for supervised |
204 | processes that use socket-based activation. This environment | |
205 | variable specifies the data | |
206 | <function>sd_listen_fds()</function> and | |
207 | <function>sd_listen_fds_with_names()</function> parses. See | |
208 | above for details.</para></listitem> | |
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209 | </varlistentry> |
210 | </variablelist> | |
211 | </refsect1> | |
212 | ||
213 | <refsect1> | |
214 | <title>See Also</title> | |
215 | ||
216 | <para> | |
217 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
218 | <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
219 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
220 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
221 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
222 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
8dd4c05b | 223 | <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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224 | <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
225 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
226 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
227 | </para> | |
228 | </refsect1> | |
f9378423 LP |
229 | |
230 | </refentry> |