]>
Commit | Line | Data |
---|---|---|
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" |
798d3a52 ZJS |
7 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
8 | ||
9 | <refentryinfo> | |
10 | <title>sd_listen_fds</title> | |
11 | <productname>systemd</productname> | |
798d3a52 ZJS |
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> |
798d3a52 ZJS |
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> | |
8dd4c05b LP |
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> | |
798d3a52 ZJS |
42 | </funcsynopsis> |
43 | </refsynopsisdiv> | |
44 | ||
45 | <refsect1> | |
46 | <title>Description</title> | |
47 | ||
8dd4c05b LP |
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 |
8dd4c05b LP |
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> |
798d3a52 | 56 | |
df2f5817 LP |
57 | <para>If a daemon receives more than one file descriptor, they will be passed in the same order as |
58 | configured in the systemd socket unit file (see | |
59 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> for | |
60 | details) — if there's only one such file (see below). Nonetheless, it is recommended to verify the | |
61 | correct socket types before using them. To simplify this checking, the functions | |
798d3a52 ZJS |
62 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
63 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
64 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
df2f5817 LP |
65 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry> are |
66 | provided. In order to maximize flexibility, it is recommended to make these checks as loose as possible | |
67 | without allowing incorrect setups. i.e. often, the actual port number a socket is bound to matters little | |
68 | for the service to work, hence it should not be verified. On the other hand, whether a socket is a | |
69 | datagram or stream socket matters a lot for the most common program logics and should be checked.</para> | |
798d3a52 ZJS |
70 | |
71 | <para>This function call will set the FD_CLOEXEC flag for all | |
72 | passed file descriptors to avoid further inheritance to children | |
73 | of the calling process.</para> | |
74 | ||
b938cb90 | 75 | <para>If multiple socket units activate the same service, the order |
798d3a52 ZJS |
76 | of the file descriptors passed to its main process is undefined. |
77 | If additional file descriptors have been passed to the service | |
78 | manager using | |
79 | <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s | |
80 | <literal>FDSTORE=1</literal> messages, these file descriptors are | |
81 | passed last, in arbitrary order, and with duplicates | |
82 | removed.</para> | |
8dd4c05b LP |
83 | |
84 | <para>If the <parameter>unset_environment</parameter> parameter is | |
85 | non-zero, <function>sd_listen_fds()</function> will unset the | |
86 | <varname>$LISTEN_FDS</varname>, <varname>$LISTEN_PID</varname> and | |
87 | <varname>$LISTEN_FDNAMES</varname> environment variables before | |
88 | returning (regardless of whether the function call itself | |
89 | succeeded or not). Further calls to | |
90 | <function>sd_listen_fds()</function> will then return zero, but the | |
91 | variables are no longer inherited by child processes.</para> | |
92 | ||
93 | <para><function>sd_listen_fds_with_names()</function> is like | |
b938cb90 | 94 | <function>sd_listen_fds()</function>, but optionally also returns |
8dd4c05b | 95 | an array of strings with identification names for the passed file |
b938cb90 | 96 | descriptors, if that is available and the |
8dd4c05b LP |
97 | <parameter>names</parameter> parameter is non-NULL. This |
98 | information is read from the <varname>$LISTEN_FDNAMES</varname> | |
99 | variable, which may contain a colon-separated list of names. For | |
100 | socket-activated services, these names may be configured with the | |
101 | <varname>FileDescriptorName=</varname> setting in socket unit | |
102 | files, see | |
103 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
104 | for details. For file descriptors pushed into the file descriptor | |
b938cb90 | 105 | store (see above), the name is set via the |
8dd4c05b LP |
106 | <varname>FDNAME=</varname> field transmitted via |
107 | <function>sd_pid_notify_with_fds()</function>. The primary usecase | |
108 | for these names are services which accept a variety of file | |
109 | descriptors which are not recognizable with functions like | |
110 | <function>sd_is_socket()</function> alone, and thus require | |
111 | identification via a name. It is recommended to rely on named file | |
112 | descriptors only if identification via | |
113 | <function>sd_is_socket()</function> and related calls is not | |
114 | sufficient. Note that the names used are not unique in any | |
115 | way. The returned array of strings has as many entries as file | |
a8eaaee7 | 116 | descriptors have been received, plus a final NULL pointer |
8dd4c05b | 117 | terminating the array. The caller needs to free the array itself |
ba6bfc0d | 118 | and each of its elements with libc's <function>free()</function> |
8dd4c05b | 119 | call after use. If the <parameter>names</parameter> parameter is |
b938cb90 | 120 | NULL, the call is entirely equivalent to |
8dd4c05b LP |
121 | <function>sd_listen_fds()</function>.</para> |
122 | ||
b938cb90 | 123 | <para>Under specific conditions, the following automatic file |
8dd4c05b LP |
124 | descriptor names are returned: |
125 | ||
126 | <table> | |
127 | <title> | |
128 | <command>Special names</command> | |
129 | </title> | |
130 | ||
131 | <tgroup cols='2'> | |
132 | <thead> | |
133 | <row> | |
134 | <entry>Name</entry> | |
135 | <entry>Description</entry> | |
136 | </row> | |
137 | </thead> | |
138 | <tbody> | |
139 | <row> | |
140 | <entry><literal>unknown</literal></entry> | |
141 | <entry>The process received no name for the specific file descriptor from the service manager.</entry> | |
142 | </row> | |
143 | ||
144 | <row> | |
145 | <entry><literal>stored</literal></entry> | |
146 | <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> | |
147 | </row> | |
148 | ||
149 | <row> | |
150 | <entry><literal>connection</literal></entry> | |
151 | <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> | |
152 | </row> | |
153 | </tbody> | |
154 | </tgroup> | |
155 | </table> | |
156 | </para> | |
798d3a52 ZJS |
157 | </refsect1> |
158 | ||
159 | <refsect1> | |
160 | <title>Return Value</title> | |
161 | ||
8dd4c05b | 162 | <para>On failure, these calls returns a negative errno-style error |
798d3a52 ZJS |
163 | code. If |
164 | <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> was | |
165 | not set or was not correctly set for this daemon and hence no file | |
166 | descriptors were received, 0 is returned. Otherwise, the number of | |
167 | file descriptors passed is returned. The application may find them | |
168 | starting with file descriptor SD_LISTEN_FDS_START, i.e. file | |
169 | descriptor 3.</para> | |
170 | </refsect1> | |
171 | ||
172 | <refsect1> | |
173 | <title>Notes</title> | |
174 | ||
175 | <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/> | |
176 | ||
8dd4c05b LP |
177 | <para>Internally, <function>sd_listen_fds()</function> checks |
178 | whether the <varname>$LISTEN_PID</varname> environment variable | |
179 | equals the daemon PID. If not, it returns immediately. Otherwise, | |
180 | it parses the number passed in the <varname>$LISTEN_FDS</varname> | |
798d3a52 ZJS |
181 | environment variable, then sets the FD_CLOEXEC flag for the parsed |
182 | number of file descriptors starting from SD_LISTEN_FDS_START. | |
8dd4c05b LP |
183 | Finally, it returns the parsed |
184 | number. <function>sd_listen_fds_with_names()</function> does the | |
185 | same but also parses <varname>$LISTEN_FDNAMES</varname> if | |
186 | set.</para> | |
798d3a52 ZJS |
187 | </refsect1> |
188 | ||
189 | <refsect1> | |
190 | <title>Environment</title> | |
191 | ||
192 | <variablelist class='environment-variables'> | |
193 | <varlistentry> | |
194 | <term><varname>$LISTEN_PID</varname></term> | |
195 | <term><varname>$LISTEN_FDS</varname></term> | |
8dd4c05b | 196 | <term><varname>$LISTEN_FDNAMES</varname></term> |
798d3a52 | 197 | |
8dd4c05b LP |
198 | <listitem><para>Set by the service manager for supervised |
199 | processes that use socket-based activation. This environment | |
200 | variable specifies the data | |
201 | <function>sd_listen_fds()</function> and | |
202 | <function>sd_listen_fds_with_names()</function> parses. See | |
203 | above for details.</para></listitem> | |
798d3a52 ZJS |
204 | </varlistentry> |
205 | </variablelist> | |
206 | </refsect1> | |
207 | ||
208 | <refsect1> | |
209 | <title>See Also</title> | |
210 | ||
211 | <para> | |
212 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
213 | <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
214 | <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
215 | <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
216 | <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
217 | <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
8dd4c05b | 218 | <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
798d3a52 ZJS |
219 | <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
220 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
221 | <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
222 | </para> | |
223 | </refsect1> | |
f9378423 LP |
224 | |
225 | </refentry> |