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01448ff9 | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
eea10b26 | 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> |
db9ecf05 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
01448ff9 | 5 | |
6a70f3aa | 6 | <refentry id="sd-login" conditional='HAVE_PAM' |
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7 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
8 | ||
9 | <refentryinfo> | |
10 | <title>sd-login</title> | |
11 | <productname>systemd</productname> | |
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12 | </refentryinfo> |
13 | ||
14 | <refmeta> | |
15 | <refentrytitle>sd-login</refentrytitle> | |
16 | <manvolnum>3</manvolnum> | |
17 | </refmeta> | |
18 | ||
19 | <refnamediv> | |
20 | <refname>sd-login</refname> | |
21 | <refpurpose>APIs for | |
22 | tracking logins</refpurpose> | |
23 | </refnamediv> | |
24 | ||
25 | <refsynopsisdiv> | |
26 | <funcsynopsis> | |
27 | <funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo> | |
28 | </funcsynopsis> | |
29 | ||
30 | <cmdsynopsis> | |
31 | <command>pkg-config --cflags --libs libsystemd</command> | |
32 | </cmdsynopsis> | |
33 | </refsynopsisdiv> | |
34 | ||
35 | <refsect1> | |
36 | <title>Description</title> | |
37 | ||
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38 | <para><filename>sd-login.h</filename> is part of |
39 | <citerefentry><refentrytitle>libsystemd</refentrytitle><manvolnum>3</manvolnum></citerefentry> and | |
40 | provides APIs to introspect and monitor seat, login session, and user status information on the local | |
41 | system.</para> | |
798d3a52 | 42 | |
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43 | <para>Note that these APIs only allow purely passive access and |
44 | monitoring of seats, sessions and users. To actively make changes | |
45 | to the seat configuration, terminate login sessions, or switch | |
46 | session on a seat you need to utilize the D-Bus API of | |
47 | systemd-logind, instead.</para> | |
48 | ||
49 | <para>These functions synchronously access data in | |
3b121157 ZJS |
50 | <filename>/proc/</filename>, <filename>/sys/fs/cgroup/</filename> |
51 | and <filename>/run/</filename>. All of these are virtual file | |
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52 | systems, hence the runtime cost of the accesses is relatively |
53 | cheap.</para> | |
54 | ||
55 | <para>It is possible (and often a very good choice) to mix calls | |
56 | to the synchronous interface of <filename>sd-login.h</filename> | |
57 | with the asynchronous D-Bus interface of systemd-logind. However, | |
58 | if this is done you need to think a bit about possible races since | |
59 | the stream of events from D-Bus and from | |
60 | <filename>sd-login.h</filename> interfaces such as the login | |
61 | monitor are asynchronous and not ordered against each | |
62 | other.</para> | |
63 | ||
64 | <para>If the functions return string arrays, these are generally | |
65 | <constant>NULL</constant> terminated and need to be freed by the | |
66 | caller with the libc | |
67 | <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
68 | call after use, including the strings referenced therein. | |
69 | Similarly, individual strings returned need to be freed, as | |
70 | well.</para> | |
71 | ||
72 | <para>As a special exception, instead of an empty string array | |
73 | <constant>NULL</constant> may be returned, which should be treated | |
74 | equivalent to an empty string array.</para> | |
75 | ||
76 | <para>See | |
77 | <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
78 | <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
79 | <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
80 | <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
81 | <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
82 | <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
83 | for more information about the functions | |
84 | implemented.</para> | |
85 | </refsect1> | |
86 | ||
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87 | <refsect1> |
88 | <title>Definition of Terms</title> | |
89 | ||
90 | <variablelist> | |
91 | <varlistentry> | |
92 | <term>seat</term> | |
93 | ||
94 | <listitem><para>A seat consists of all hardware devices assigned to a specific | |
95 | workplace. It consists of at least one graphics device, and usually also includes | |
96 | keyboard, mouse. It can also include video cameras, sound cards and more. Seats | |
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97 | are identified by seat names, which are strings (<= 255 characters), that start |
98 | with the four characters <literal>seat</literal> followed by at least one | |
0ae42c9b | 99 | character from the range [a-zA-Z0-9], <literal>_</literal> and |
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100 | <literal>-</literal>. They are suitable for use as file names. Seat names may or |
101 | may not be stable and may be reused if a seat becomes available again. | |
ec07c3c8 AK |
102 | </para> |
103 | ||
104 | <xi:include href="version-info.xml" xpointer="v235"/></listitem> | |
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105 | </varlistentry> |
106 | ||
107 | <varlistentry> | |
108 | <term>session</term> | |
109 | ||
110 | <listitem><para>A session is defined by the time a user is logged in until they | |
111 | log out. A session is bound to one or no seats (the latter for 'virtual' ssh | |
112 | logins). Multiple sessions can be attached to the same seat, but only one of them | |
113 | can be active, the others are in the background. A session is identified by a | |
114 | short string.</para> | |
115 | ||
116 | <para> | |
117 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
118 | ensures that audit sessions are identical to systemd sessions, and uses the audit | |
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119 | session ID as session ID in systemd (if auditing is enabled). In general the |
120 | session identifier is a short string consisting only of [a-zA-Z0-9], | |
121 | <literal>_</literal> and <literal>-</literal>, suitable for use as a file name. | |
122 | Session IDs are unique on the local machine and are | |
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123 | never reused as long as the machine is online. A user (the way we know it on UNIX) |
124 | corresponds to the person using a computer. A single user can have multiple | |
125 | sessions open at the same time. A user is identified by a numeric user id (UID) or | |
126 | a user name (a string). A multi-session system allows multiple user sessions on | |
127 | the same seat at the same time. A multi-seat system allows multiple independent | |
128 | seats that can be individually and simultaneously used by different users.</para> | |
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129 | |
130 | <xi:include href="version-info.xml" xpointer="v235"/> | |
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131 | </listitem> |
132 | </varlistentry> | |
133 | </variablelist> | |
134 | ||
135 | <para>All hardware devices that are eligible to being assigned to a seat, are assigned | |
136 | to one. A device can be assigned to only one seat at a time. If a device is not | |
137 | assigned to any particular other seat it is implicitly assigned to the special default | |
138 | seat called <literal>seat0</literal>.</para> | |
139 | ||
140 | <para>Note that hardware like printers, hard disks or network cards is generally not | |
141 | assigned to a specific seat. They are available to all seats equally. (Well, with one | |
142 | exception: USB sticks can be assigned to a seat.)</para> | |
143 | ||
144 | <para><literal>seat0</literal> always exists.</para> | |
145 | </refsect1> | |
146 | ||
147 | <refsect1> | |
148 | <title>udev Rules</title> | |
149 | ||
150 | <para>Assignment of hardware devices to seats is managed inside the udev database, via | |
151 | settings on the devices:</para> | |
152 | ||
6772ce6e | 153 | <variablelist class='udev-directives'> |
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154 | <varlistentry> |
155 | <term>Tag <literal>seat</literal></term> | |
156 | ||
157 | <listitem><para>When set, a device is eligible to be assigned to a seat. This tag | |
158 | is set for graphics devices, mice, keyboards, video cards, sound cards and | |
159 | more. Note that some devices like sound cards consist of multiple subdevices | |
160 | (i.e. a PCM for input and another one for output). This tag will be set only for | |
161 | the originating device, not for the individual subdevices. A UI for configuring | |
162 | assignment of devices to seats should enumerate and subscribe to all devices with | |
163 | this tag set and show them in the UI. Note that USB hubs can be assigned to a seat | |
164 | as well, in which case all (current and future) devices plugged into it will also | |
165 | be assigned to the same seat (unless they are explicitly assigned to another | |
166 | seat). | |
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167 | </para> |
168 | ||
169 | <xi:include href="version-info.xml" xpointer="v235"/></listitem> | |
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170 | </varlistentry> |
171 | ||
172 | <varlistentry> | |
173 | <term>Tag <literal>master-of-seat</literal></term> | |
174 | ||
175 | <listitem><para>When set, this device is enough for a seat to be considered | |
176 | existent. This tag is usually set for the framebuffer device of graphics cards. A | |
177 | seat hence consists of an arbitrary number of devices marked with the | |
178 | <literal>seat</literal> tag, but (at least) one of these devices needs to be | |
179 | tagged with <literal>master-of-seat</literal> before the seat is actually | |
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180 | considered to be around.</para> |
181 | ||
182 | <xi:include href="version-info.xml" xpointer="v235"/></listitem> | |
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183 | </varlistentry> |
184 | ||
185 | <varlistentry> | |
186 | <term>Property <varname>ID_SEAT</varname></term> | |
187 | ||
188 | <listitem><para>This property specifies the name of the seat a specific device is | |
189 | assigned to. If not set the device is assigned to <literal>seat0</literal>. Also, | |
190 | to speed up enumeration of hardware belonging to a specific seat, the seat is also | |
191 | set as tag on the device. I.e. if the property | |
192 | <varname>ID_SEAT=seat-waldo</varname> is set for a device, the tag | |
193 | <literal>seat-waldo</literal> will be set as well. Note that if a device is | |
194 | assigned to <literal>seat0</literal>, it will usually not carry such a tag and you | |
195 | need to enumerate all devices and check the <varname>ID_SEAT</varname> property | |
196 | manually. Again, if a device is assigned to seat0 this is visible on the device in | |
197 | two ways: with a property <varname>ID_SEAT=seat0</varname> and with no property | |
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198 | <varname>ID_SEAT</varname> set for it at all.</para> |
199 | ||
200 | <xi:include href="version-info.xml" xpointer="v235"/></listitem> | |
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201 | </varlistentry> |
202 | ||
203 | <varlistentry> | |
204 | <term>Property <varname>ID_AUTOSEAT</varname></term> | |
205 | ||
206 | <listitem><para>When set to <literal>1</literal>, this device automatically | |
207 | generates a new and independent seat, which is named after the path of the | |
86b52a39 | 208 | device. This is set for specialized USB hubs like the Pluggable devices, which when |
0ae42c9b | 209 | plugged in should create a hotplug seat without further configuration.</para> |
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210 | |
211 | <xi:include href="version-info.xml" xpointer="v235"/> | |
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212 | </listitem> |
213 | </varlistentry> | |
214 | ||
215 | <varlistentry> | |
216 | <term>Property <varname>ID_FOR_SEAT</varname></term> | |
217 | ||
218 | <listitem><para>When creating additional (manual) seats starting from a graphics | |
219 | device this is a good choice to name the seat after. It is created from the path | |
220 | of the device. This is useful in UIs for configuring seats: as soon as you create | |
221 | a new seat from a graphics device, read this property and prefix it with | |
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222 | <literal>seat-</literal> and use it as name for the seat.</para> |
223 | ||
224 | <xi:include href="version-info.xml" xpointer="v235"/></listitem> | |
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225 | </varlistentry> |
226 | </variablelist> | |
227 | ||
228 | <para>A seat exists only and exclusively because a properly tagged device with the | |
229 | right <varname>ID_SEAT</varname> property exists. Besides udev rules there is no | |
230 | persistent data about seats stored on disk.</para> | |
231 | ||
232 | <para>Note that | |
233 | <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
234 | manages ACLs on a number of device classes, to allow user code to access the device | |
235 | nodes attached to a seat as long as the user has an active session on it. This is | |
236 | mostly transparent to applications. As mentioned above, for certain user software it | |
237 | might be a good idea to watch whether they can access device nodes instead of thinking | |
238 | about seats.</para> | |
239 | </refsect1> | |
240 | ||
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241 | <xi:include href="libsystemd-pkgconfig.xml" /> |
242 | ||
243 | <refsect1> | |
244 | <title>See Also</title> | |
13a69c12 DT |
245 | <para><simplelist type="inline"> |
246 | <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> | |
247 | <member><citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
248 | <member><citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
249 | <member><citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
250 | <member><citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
251 | <member><citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
252 | <member><citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
253 | <member><citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
254 | <member><citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> | |
255 | </simplelist></para> | |
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256 | |
257 | <para> | |
258 | <ulink url="https://www.freedesktop.org/wiki/Software/systemd/multiseat">Multi-Seat on Linux</ulink> | |
515736d0 | 259 | may also be of historical interest. |
0ae42c9b | 260 | </para> |
798d3a52 | 261 | </refsect1> |
01448ff9 | 262 | </refentry> |