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514094f9 | 1 | <?xml version='1.0'?> |
f9378423 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
6a70f3aa | 9 | <refentry id="sd_listen_fds" |
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10 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
11 | ||
12 | <refentryinfo> | |
13 | <title>sd_listen_fds</title> | |
14 | <productname>systemd</productname> | |
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15 | </refentryinfo> |
16 | ||
17 | <refmeta> | |
18 | <refentrytitle>sd_listen_fds</refentrytitle> | |
19 | <manvolnum>3</manvolnum> | |
20 | </refmeta> | |
21 | ||
22 | <refnamediv> | |
23 | <refname>sd_listen_fds</refname> | |
8dd4c05b | 24 | <refname>sd_listen_fds_with_names</refname> |
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25 | <refname>SD_LISTEN_FDS_START</refname> |
26 | <refpurpose>Check for file descriptors passed by the system manager</refpurpose> | |
27 | </refnamediv> | |
28 | ||
29 | <refsynopsisdiv> | |
30 | <funcsynopsis> | |
31 | <funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo> | |
32 | ||
33 | <funcsynopsisinfo>#define SD_LISTEN_FDS_START 3</funcsynopsisinfo> | |
34 | ||
35 | <funcprototype> | |
36 | <funcdef>int <function>sd_listen_fds</function></funcdef> | |
37 | <paramdef>int <parameter>unset_environment</parameter></paramdef> | |
38 | </funcprototype> | |
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39 | |
40 | <funcprototype> | |
41 | <funcdef>int <function>sd_listen_fds_with_names</function></funcdef> | |
42 | <paramdef>int <parameter>unset_environment</parameter></paramdef> | |
43 | <paramdef>char*** <parameter>names</parameter></paramdef> | |
44 | </funcprototype> | |
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45 | </funcsynopsis> |
46 | </refsynopsisdiv> | |
47 | ||
48 | <refsect1> | |
49 | <title>Description</title> | |
50 | ||
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51 | <para><function>sd_listen_fds()</function> may be invoked by a |
52 | daemon to check for file descriptors passed by the service manager as | |
53 | part of the socket-based activation logic. It returns the number | |
54 | of received file descriptors. If no file descriptors have been | |
b938cb90 | 55 | received, zero is returned. The first file descriptor may be found |
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56 | at file descriptor number 3 |
57 | (i.e. <constant>SD_LISTEN_FDS_START</constant>), the remaining | |
1eecafb8 | 58 | descriptors follow at 4, 5, 6, …, if any.</para> |
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59 | |
60 | <para>If a daemon receives more than one file descriptor, they | |
61 | will be passed in the same order as configured in the systemd | |
62 | socket unit file (see | |
63 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
64 | for details). Nonetheless, it is recommended to verify the correct | |
65 | socket types before using them. To simplify this checking, the | |
66 | functions | |
67 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
68 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
69 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
70 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
71 | are provided. In order to maximize flexibility, it is recommended | |
72 | to make these checks as loose as possible without allowing | |
73 | incorrect setups. i.e. often, the actual port number a socket is | |
74 | bound to matters little for the service to work, hence it should | |
75 | not be verified. On the other hand, whether a socket is a datagram | |
76 | or stream socket matters a lot for the most common program logics | |
77 | and should be checked.</para> | |
78 | ||
79 | <para>This function call will set the FD_CLOEXEC flag for all | |
80 | passed file descriptors to avoid further inheritance to children | |
81 | of the calling process.</para> | |
82 | ||
b938cb90 | 83 | <para>If multiple socket units activate the same service, the order |
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84 | of the file descriptors passed to its main process is undefined. |
85 | If additional file descriptors have been passed to the service | |
86 | manager using | |
87 | <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s | |
88 | <literal>FDSTORE=1</literal> messages, these file descriptors are | |
89 | passed last, in arbitrary order, and with duplicates | |
90 | removed.</para> | |
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91 | |
92 | <para>If the <parameter>unset_environment</parameter> parameter is | |
93 | non-zero, <function>sd_listen_fds()</function> will unset the | |
94 | <varname>$LISTEN_FDS</varname>, <varname>$LISTEN_PID</varname> and | |
95 | <varname>$LISTEN_FDNAMES</varname> environment variables before | |
96 | returning (regardless of whether the function call itself | |
97 | succeeded or not). Further calls to | |
98 | <function>sd_listen_fds()</function> will then return zero, but the | |
99 | variables are no longer inherited by child processes.</para> | |
100 | ||
101 | <para><function>sd_listen_fds_with_names()</function> is like | |
b938cb90 | 102 | <function>sd_listen_fds()</function>, but optionally also returns |
8dd4c05b | 103 | an array of strings with identification names for the passed file |
b938cb90 | 104 | descriptors, if that is available and the |
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105 | <parameter>names</parameter> parameter is non-NULL. This |
106 | information is read from the <varname>$LISTEN_FDNAMES</varname> | |
107 | variable, which may contain a colon-separated list of names. For | |
108 | socket-activated services, these names may be configured with the | |
109 | <varname>FileDescriptorName=</varname> setting in socket unit | |
110 | files, see | |
111 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
112 | for details. For file descriptors pushed into the file descriptor | |
b938cb90 | 113 | store (see above), the name is set via the |
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114 | <varname>FDNAME=</varname> field transmitted via |
115 | <function>sd_pid_notify_with_fds()</function>. The primary usecase | |
116 | for these names are services which accept a variety of file | |
117 | descriptors which are not recognizable with functions like | |
118 | <function>sd_is_socket()</function> alone, and thus require | |
119 | identification via a name. It is recommended to rely on named file | |
120 | descriptors only if identification via | |
121 | <function>sd_is_socket()</function> and related calls is not | |
122 | sufficient. Note that the names used are not unique in any | |
123 | way. The returned array of strings has as many entries as file | |
a8eaaee7 | 124 | descriptors have been received, plus a final NULL pointer |
8dd4c05b | 125 | terminating the array. The caller needs to free the array itself |
ba6bfc0d | 126 | and each of its elements with libc's <function>free()</function> |
8dd4c05b | 127 | call after use. If the <parameter>names</parameter> parameter is |
b938cb90 | 128 | NULL, the call is entirely equivalent to |
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129 | <function>sd_listen_fds()</function>.</para> |
130 | ||
b938cb90 | 131 | <para>Under specific conditions, the following automatic file |
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132 | descriptor names are returned: |
133 | ||
134 | <table> | |
135 | <title> | |
136 | <command>Special names</command> | |
137 | </title> | |
138 | ||
139 | <tgroup cols='2'> | |
140 | <thead> | |
141 | <row> | |
142 | <entry>Name</entry> | |
143 | <entry>Description</entry> | |
144 | </row> | |
145 | </thead> | |
146 | <tbody> | |
147 | <row> | |
148 | <entry><literal>unknown</literal></entry> | |
149 | <entry>The process received no name for the specific file descriptor from the service manager.</entry> | |
150 | </row> | |
151 | ||
152 | <row> | |
153 | <entry><literal>stored</literal></entry> | |
154 | <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> | |
155 | </row> | |
156 | ||
157 | <row> | |
158 | <entry><literal>connection</literal></entry> | |
159 | <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> | |
160 | </row> | |
161 | </tbody> | |
162 | </tgroup> | |
163 | </table> | |
164 | </para> | |
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165 | </refsect1> |
166 | ||
167 | <refsect1> | |
168 | <title>Return Value</title> | |
169 | ||
8dd4c05b | 170 | <para>On failure, these calls returns a negative errno-style error |
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171 | code. If |
172 | <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> was | |
173 | not set or was not correctly set for this daemon and hence no file | |
174 | descriptors were received, 0 is returned. Otherwise, the number of | |
175 | file descriptors passed is returned. The application may find them | |
176 | starting with file descriptor SD_LISTEN_FDS_START, i.e. file | |
177 | descriptor 3.</para> | |
178 | </refsect1> | |
179 | ||
180 | <refsect1> | |
181 | <title>Notes</title> | |
182 | ||
183 | <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/> | |
184 | ||
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185 | <para>Internally, <function>sd_listen_fds()</function> checks |
186 | whether the <varname>$LISTEN_PID</varname> environment variable | |
187 | equals the daemon PID. If not, it returns immediately. Otherwise, | |
188 | it parses the number passed in the <varname>$LISTEN_FDS</varname> | |
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189 | environment variable, then sets the FD_CLOEXEC flag for the parsed |
190 | number of file descriptors starting from SD_LISTEN_FDS_START. | |
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191 | Finally, it returns the parsed |
192 | number. <function>sd_listen_fds_with_names()</function> does the | |
193 | same but also parses <varname>$LISTEN_FDNAMES</varname> if | |
194 | set.</para> | |
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195 | </refsect1> |
196 | ||
197 | <refsect1> | |
198 | <title>Environment</title> | |
199 | ||
200 | <variablelist class='environment-variables'> | |
201 | <varlistentry> | |
202 | <term><varname>$LISTEN_PID</varname></term> | |
203 | <term><varname>$LISTEN_FDS</varname></term> | |
8dd4c05b | 204 | <term><varname>$LISTEN_FDNAMES</varname></term> |
798d3a52 | 205 | |
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206 | <listitem><para>Set by the service manager for supervised |
207 | processes that use socket-based activation. This environment | |
208 | variable specifies the data | |
209 | <function>sd_listen_fds()</function> and | |
210 | <function>sd_listen_fds_with_names()</function> parses. See | |
211 | above for details.</para></listitem> | |
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212 | </varlistentry> |
213 | </variablelist> | |
214 | </refsect1> | |
215 | ||
216 | <refsect1> | |
217 | <title>See Also</title> | |
218 | ||
219 | <para> | |
220 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
221 | <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
222 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
223 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
224 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
225 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
8dd4c05b | 226 | <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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227 | <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
228 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
229 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
230 | </para> | |
231 | </refsect1> | |
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232 | |
233 | </refentry> |