mirror of
https://github.com/systemd/systemd.git
synced 2024-11-01 17:51:22 +03:00
248 lines
12 KiB
XML
248 lines
12 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
|
<!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-or-later -->
|
|
|
|
<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>
|
|
may also be of historical interest.
|
|
</para>
|
|
</refsect1>
|
|
</refentry>
|