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diff --git a/man/sd-login.xml b/man/sd-login.xml new file mode 100644 index 0000000..3743957 --- /dev/null +++ b/man/sd-login.xml @@ -0,0 +1,251 @@ +<?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"> + +<!-- + 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 Plugable 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> |