<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
- "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
-<!--
- This file is part of systemd.
-
- Copyright 2010 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
-
-<refentry id="sd-login" conditional='HAVE_PAM'>
-
- <refentryinfo>
- <title>sd-login</title>
- <productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
- </refentryinfo>
-
- <refmeta>
- <refentrytitle>sd-login</refentrytitle>
- <manvolnum>3</manvolnum>
- </refmeta>
-
- <refnamediv>
- <refname>sd-login</refname>
- <refpurpose>APIs for
- tracking logins</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo>
- </funcsynopsis>
-
- <cmdsynopsis>
- <command>pkg-config --cflags --libs libsystemd-login</command>
- </cmdsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para><filename>sd-login.h</filename> provides APIs to
- introspect and monitor seat, login session and user
- status information on the local system. </para>
-
- <para>See <ulink
- url="http://www.freedesktop.org/wiki/Software/systemd/multiseat">Multi-Seat
- on Linux</ulink> for an introduction into multi-seat
- support on Linux, the background for this set of APIs.</para>
-
- <para>Note that these APIs only allow purely passive access
- and monitoring of seats, sessions and users. To
- actively make changes to the seat configuration,
- terminate login sessions, or switch session on a seat
- you need to utilize the D-Bus API of
- systemd-logind, instead.</para>
-
- <para>These functions synchronously access data in
- <filename>/proc</filename>,
- <filename>/sys/fs/cgroup</filename> and
- <filename>/run</filename>. All of these are virtual
- file systems, hence the runtime cost of the accesses
- is relatively cheap.</para>
-
- <para>It is possible (and often a very good choice) to
- mix calls to the synchronous interface of
- <filename>sd-login.h</filename> with the asynchronous
- D-Bus interface of systemd-logind. However, if this is
- done you need to think a bit about possible races
- since the stream of events from D-Bus and from
- <filename>sd-login.h</filename> interfaces such as the
- login monitor are asynchronous and not ordered against
- each other.</para>
-
- <para>If the functions return string arrays, these are
- generally <constant>NULL</constant> terminated and need to be freed by the
- caller with the libc
- <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- call after use, including the strings referenced
- therein. Similarly, individual strings returned need to
- be freed, as well.</para>
-
- <para>As a special exception, instead of an empty
- string array <constant>NULL</constant> may be returned, which should be
- treated equivalent to an empty string array.</para>
-
- <para>See
- <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- for more information about the functions
- implemented.</para>
- </refsect1>
-
- <refsect1>
- <title>Notes</title>
-
- <para>These APIs are implemented as a shared library,
- which can be compiled and linked to with the
- <constant>libsystemd-login</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- file.</para>
- </refsect1>
-
- <refsect1>
- <title>See Also</title>
- <para>
- <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- </para>
- </refsect1>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
+
+<refentry id="sd-login" conditional='HAVE_PAM'
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd-login</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd-login</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd-login</refname>
+ <refpurpose>APIs for
+ tracking logins</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo>
+ </funcsynopsis>
+
+ <cmdsynopsis>
+ <command>pkg-config --cflags --libs libsystemd</command>
+ </cmdsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><filename>sd-login.h</filename> provides APIs to introspect
+ and monitor seat, login session and user status information on the
+ local system. </para>
+
+ <para>Note that these APIs only allow purely passive access and
+ monitoring of seats, sessions and users. To actively make changes
+ to the seat configuration, terminate login sessions, or switch
+ session on a seat you need to utilize the D-Bus API of
+ systemd-logind, instead.</para>
+
+ <para>These functions synchronously access data in
+ <filename>/proc</filename>, <filename>/sys/fs/cgroup</filename>
+ and <filename>/run</filename>. All of these are virtual file
+ systems, hence the runtime cost of the accesses is relatively
+ cheap.</para>
+
+ <para>It is possible (and often a very good choice) to mix calls
+ to the synchronous interface of <filename>sd-login.h</filename>
+ with the asynchronous D-Bus interface of systemd-logind. However,
+ if this is done you need to think a bit about possible races since
+ the stream of events from D-Bus and from
+ <filename>sd-login.h</filename> interfaces such as the login
+ monitor are asynchronous and not ordered against each
+ other.</para>
+
+ <para>If the functions return string arrays, these are generally
+ <constant>NULL</constant> terminated and need to be freed by the
+ caller with the libc
+ <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ call after use, including the strings referenced therein.
+ Similarly, individual strings returned need to be freed, as
+ well.</para>
+
+ <para>As a special exception, instead of an empty string array
+ <constant>NULL</constant> may be returned, which should be treated
+ equivalent to an empty string array.</para>
+
+ <para>See
+ <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ for more information about the functions
+ implemented.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Definition of Terms</title>
+
+ <variablelist>
+ <varlistentry>
+ <term>seat</term>
+
+ <listitem><para>A seat consists of all hardware devices assigned to a specific
+ workplace. It consists of at least one graphics device, and usually also includes
+ keyboard, mouse. It can also include video cameras, sound cards and more. Seats
+ are identified by seat names, which are strings (<= 255 characters), that start
+ with the four characters <literal>seat</literal> followed by at least one
+ character from the range [a-zA-Z0-9], <literal>_</literal> and
+ <literal>-</literal>. They are suitable for use as file names. Seat names may or
+ may not be stable and may be reused if a seat becomes available again.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>session</term>
+
+ <listitem><para>A session is defined by the time a user is logged in until they
+ log out. A session is bound to one or no seats (the latter for 'virtual' ssh
+ logins). Multiple sessions can be attached to the same seat, but only one of them
+ can be active, the others are in the background. A session is identified by a
+ short string.</para>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ ensures that audit sessions are identical to systemd sessions, and uses the audit
+ session ID as session ID in systemd (if auditing is enabled). In general the
+ session identifier is a short string consisting only of [a-zA-Z0-9],
+ <literal>_</literal> and <literal>-</literal>, suitable for use as a file name.
+ Session IDs are unique on the local machine and are
+ never reused as long as the machine is online. A user (the way we know it on UNIX)
+ corresponds to the person using a computer. A single user can have multiple
+ sessions open at the same time. A user is identified by a numeric user id (UID) or
+ a user name (a string). A multi-session system allows multiple user sessions on
+ the same seat at the same time. A multi-seat system allows multiple independent
+ seats that can be individually and simultaneously used by different users.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>All hardware devices that are eligible to being assigned to a seat, are assigned
+ to one. A device can be assigned to only one seat at a time. If a device is not
+ assigned to any particular other seat it is implicitly assigned to the special default
+ seat called <literal>seat0</literal>.</para>
+
+ <para>Note that hardware like printers, hard disks or network cards is generally not
+ assigned to a specific seat. They are available to all seats equally. (Well, with one
+ exception: USB sticks can be assigned to a seat.)</para>
+
+ <para><literal>seat0</literal> always exists.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>udev Rules</title>
+
+ <para>Assignment of hardware devices to seats is managed inside the udev database, via
+ settings on the devices:</para>
+
+ <variablelist class='udev-directives'>
+ <varlistentry>
+ <term>Tag <literal>seat</literal></term>
+
+ <listitem><para>When set, a device is eligible to be assigned to a seat. This tag
+ is set for graphics devices, mice, keyboards, video cards, sound cards and
+ more. Note that some devices like sound cards consist of multiple subdevices
+ (i.e. a PCM for input and another one for output). This tag will be set only for
+ the originating device, not for the individual subdevices. A UI for configuring
+ assignment of devices to seats should enumerate and subscribe to all devices with
+ this tag set and show them in the UI. Note that USB hubs can be assigned to a seat
+ as well, in which case all (current and future) devices plugged into it will also
+ be assigned to the same seat (unless they are explicitly assigned to another
+ seat).
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Tag <literal>master-of-seat</literal></term>
+
+ <listitem><para>When set, this device is enough for a seat to be considered
+ existent. This tag is usually set for the framebuffer device of graphics cards. A
+ seat hence consists of an arbitrary number of devices marked with the
+ <literal>seat</literal> tag, but (at least) one of these devices needs to be
+ tagged with <literal>master-of-seat</literal> before the seat is actually
+ considered to be around.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Property <varname>ID_SEAT</varname></term>
+
+ <listitem><para>This property specifies the name of the seat a specific device is
+ assigned to. If not set the device is assigned to <literal>seat0</literal>. Also,
+ to speed up enumeration of hardware belonging to a specific seat, the seat is also
+ set as tag on the device. I.e. if the property
+ <varname>ID_SEAT=seat-waldo</varname> is set for a device, the tag
+ <literal>seat-waldo</literal> will be set as well. Note that if a device is
+ assigned to <literal>seat0</literal>, it will usually not carry such a tag and you
+ need to enumerate all devices and check the <varname>ID_SEAT</varname> property
+ manually. Again, if a device is assigned to seat0 this is visible on the device in
+ two ways: with a property <varname>ID_SEAT=seat0</varname> and with no property
+ <varname>ID_SEAT</varname> set for it at all.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Property <varname>ID_AUTOSEAT</varname></term>
+
+ <listitem><para>When set to <literal>1</literal>, this device automatically
+ generates a new and independent seat, which is named after the path of the
+ device. This is set for specialized USB hubs like the Pluggable devices, which when
+ plugged in should create a hotplug seat without further configuration.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Property <varname>ID_FOR_SEAT</varname></term>
+
+ <listitem><para>When creating additional (manual) seats starting from a graphics
+ device this is a good choice to name the seat after. It is created from the path
+ of the device. This is useful in UIs for configuring seats: as soon as you create
+ a new seat from a graphics device, read this property and prefix it with
+ <literal>seat-</literal> and use it as name for the seat.</para></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>A seat exists only and exclusively because a properly tagged device with the
+ right <varname>ID_SEAT</varname> property exists. Besides udev rules there is no
+ persistent data about seats stored on disk.</para>
+
+ <para>Note that
+ <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ manages ACLs on a number of device classes, to allow user code to access the device
+ nodes attached to a seat as long as the user has an active session on it. This is
+ mostly transparent to applications. As mentioned above, for certain user software it
+ might be a good idea to watch whether they can access device nodes instead of thinking
+ about seats.</para>
+ </refsect1>
+
+ <xi:include href="libsystemd-pkgconfig.xml" />
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ </para>
+
+ <para>
+ <ulink url="https://www.freedesktop.org/wiki/Software/systemd/multiseat">Multi-Seat on Linux</ulink>
+ for an introduction to multi-seat support on Linux and the background for this set of APIs.
+ </para>
+ </refsect1>
</refentry>
projects / thirdparty / systemd.git / blobdiff