man/pam_systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="pam_systemd" conditional='HAVE_PAM' xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>pam_systemd</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>pam_systemd</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>pam_systemd</refname>
  20     <refpurpose>Register user sessions in the systemd login manager</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv>
  24     <para><filename>pam_systemd.so</filename></para>
  25   </refsynopsisdiv>
  26
  27   <refsect1>
  28     <title>Description</title>
  29
  30     <para><command>pam_systemd</command> registers user sessions with
  31     the systemd login manager
  32     <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  33     and hence the systemd control group hierarchy.</para>
  34
  35     <para>The module also applies various resource management and runtime parameters to the new session, as
  36     configured in the <ulink url="https://systemd.io/USER_RECORD">JSON User Records</ulink> of the user, when
  37     one is defined.</para>
  38
  39     <para>On login, this module — in conjunction with <filename>systemd-logind.service</filename> — ensures the
  40     following:</para>
  41
  42     <orderedlist>
  43       <listitem><para>If it does not exist yet, the user runtime directory <filename>/run/user/$UID</filename> is
  44       either created or mounted as new <literal>tmpfs</literal> file system with quota applied, and its ownership
  45       changed to the user that is logging in.</para></listitem>
  46
  47       <listitem><para>The <varname>$XDG_SESSION_ID</varname> environment variable is initialized. If auditing is
  48       available and <command>pam_loginuid.so</command> was run before this module (which is highly recommended), the
  49       variable is initialized from the auditing session id (<filename>/proc/self/sessionid</filename>). Otherwise, an
  50       independent session counter is used.</para></listitem>
  51
  52       <listitem><para>A new systemd scope unit is created for the session. If this is the first concurrent session of
  53       the user, an implicit per-user slice unit below <filename>user.slice</filename> is automatically created and the
  54       scope placed into it. An instance of the system service <filename>user@.service</filename>, which runs the
  55       systemd user manager instance, is started.</para></listitem>
  56
  57       <listitem><para>The <literal>$TZ</literal>, <literal>$EMAIL</literal> and <literal>$LANG</literal>
  58       environment variables are configured for the user, based on the respective data from the user's JSON
  59       record (if it is defined). Moreover, any environment variables explicitly configured in the user record
  60       are imported, and the umask, nice level, and resource limits initialized.</para></listitem>
  61     </orderedlist>
  62
  63     <para>On logout, this module ensures the following:</para>
  64
  65     <orderedlist>
  66       <listitem><para>If enabled in
  67       <citerefentry><refentrytitle>logind.conf</refentrytitle>
  68       <manvolnum>5</manvolnum></citerefentry> (<varname>KillUserProcesses=</varname>), all processes of the session are
  69       terminated. If the last concurrent session of a user ends, the user's systemd instance will be terminated too,
  70       and so will the user's slice unit.</para></listitem>
  71
  72       <listitem><para>If the last concurrent session of a user ends,
  73       the user runtime directory <filename>/run/user/$UID</filename> and all its
  74       contents are removed, too.</para></listitem>
  75     </orderedlist>
  76
  77     <para>If the system was not booted up with systemd as init system,
  78     this module does nothing and immediately returns
  79     <constant>PAM_SUCCESS</constant>.</para>
  80
  81   </refsect1>
  82
  83   <refsect1>
  84     <title>Options</title>
  85
  86     <para>The following options are understood:</para>
  87
  88     <variablelist class='pam-directives'>
  89
  90       <varlistentry>
  91         <term><varname>class=</varname></term>
  92
  93         <listitem><para>Takes a string argument which sets the session class. The
  94         <varname>XDG_SESSION_CLASS</varname> environment variable (see below) takes precedence. See
  95         <citerefentry><refentrytitle>sd_session_get_class</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  96         for a way to query the class of a session. The following session classes are defined:</para>
  97
  98         <table>
  99           <title>Session Classes</title>
 100           <tgroup cols='2' align='left' colsep='1' rowsep='1'>
 101             <colspec colname="name" />
 102             <colspec colname="explanation" />
 103             <thead>
 104               <row>
 105                 <entry>Name</entry>
 106                 <entry>Explanation</entry>
 107               </row>
 108             </thead>
 109             <tbody>
 110               <row>
 111                 <entry><constant>user</constant></entry>
 112                 <entry>A regular interactive user session. This is the default class for sessions for which a TTY or X display is known at session registration time.</entry>
 113               </row>
 114               <row>
 115                 <entry><constant>user-early</constant></entry>
 116                 <entry>Similar to <literal>user</literal> but sessions of this class are not ordered after <filename>systemd-user-sessions.service</filename>, i.e. may be started before regular sessions are allowed to be established. This session class is the default for sessions of the root user that would otherwise qualify for the <constant>user</constant> class, see above. (Added in v256.)</entry>
 117               </row>
 118               <row>
 119                 <entry><constant>user-incomplete</constant></entry>
 120                 <entry>Similar to <literal>user</literal> but for sessions which are not fully set up yet, i.e. have no home directory mounted ot similar. This is used by <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> to allow users to log in via <command>ssh</command> before their home directory is mounted, delaying the mount until the user provided the unlock password. Sessions of this class are upgraded to the regular <constant>user</constant> class once the home directory is activated.</entry>
 121               </row>
 122               <row>
 123                 <entry><constant>greeter</constant></entry>
 124                 <entry>Similar to <literal>user</literal> but for sessions that are spawned by a display manager ephemerally and which prompt the user for login credentials.</entry>
 125               </row>
 126               <row>
 127                 <entry><constant>lock-screen</constant></entry>
 128                 <entry>Similar to <literal>user</literal> but for sessions that are spawned by a display manager ephemerally and which show a lock screen that can be used to unlock locked user accounts or sessions.</entry>
 129               </row>
 130               <row>
 131                 <entry><constant>background</constant></entry>
 132                 <entry>Used for background sessions, such as those invoked by <command>cron</command> and similar tools. This is the default class for sessions for which no TTY or X display is known at session registration time.</entry>
 133               </row>
 134               <row>
 135                 <entry><constant>background-light</constant></entry>
 136                 <entry>Similar to <constant>background</constant>, but sessions of this class will not pull in the <filename>user@.service</filename> of the user, and thus possibly have no services of the user running. (Added in v256.)</entry>
 137               </row>
 138               <row>
 139                 <entry><constant>manager</constant></entry>
 140                 <entry>The <filename>user@.service</filename> service of the user is registered under this session class. (Added in v256.)</entry>
 141               </row>
 142               <row>
 143                 <entry><constant>manager-early</constant></entry>
 144                 <entry>Similar to <constant>manager</constant>, but for the root user. Compare with the <constant>user</constant> vs. <constant>user-early</constant> situation. (Added in v256.)</entry>
 145               </row>
 146             </tbody>
 147           </tgroup>
 148         </table>
 149
 150         <xi:include href="version-info.xml" xpointer="v197"/></listitem>
 151       </varlistentry>
 152
 153       <varlistentry>
 154         <term><varname>type=</varname></term>
 155
 156         <listitem><para>Takes a string argument which sets the session type. The <varname>XDG_SESSION_TYPE</varname>
 157         environment variable (see below) takes precedence. One of <literal>unspecified</literal>,
 158         <literal>tty</literal>, <literal>x11</literal>, <literal>wayland</literal> or <literal>mir</literal>. See
 159         <citerefentry><refentrytitle>sd_session_get_type</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
 160         details about the session type.</para>
 161
 162         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 163       </varlistentry>
 164
 165       <varlistentry>
 166         <term><varname>desktop=</varname></term>
 167
 168         <listitem><para>Takes a single, short identifier string for the desktop environment. The
 169         <varname>XDG_SESSION_DESKTOP</varname> environment variable (see below) takes precedence. This may be used to
 170         indicate the session desktop used, where this applies and if this information is available. For example:
 171         <literal>GNOME</literal>, or <literal>KDE</literal>. It is recommended to use the same identifiers and
 172         capitalization as for <varname>$XDG_CURRENT_DESKTOP</varname>, as defined by the <ulink
 173         url="https://standards.freedesktop.org/desktop-entry-spec/latest/">Desktop Entry
 174         Specification</ulink>. (However, note that the option only takes a single item, and not a colon-separated list
 175         like <varname>$XDG_CURRENT_DESKTOP</varname>.) See
 176         <citerefentry><refentrytitle>sd_session_get_desktop</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
 177         further details.</para>
 178
 179         <xi:include href="version-info.xml" xpointer="v240"/></listitem>
 180       </varlistentry>
 181
 182       <varlistentry>
 183         <term><varname>default-capability-bounding-set=</varname></term>
 184         <term><varname>default-capability-ambient-set=</varname></term>
 185
 186         <listitem><para>Takes a comma-separated list of process capabilities
 187         (e.g. <constant>CAP_WAKE_ALARM</constant>, <constant>CAP_BLOCK_SUSPEND</constant>, …) to set for the
 188         invoked session's processes, if the user record does not encode appropriate sets of capabilities
 189         directly. See <citerefentry
 190         project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 191         for details on the capabilities concept. If not specified, the default bounding set is left as is
 192         (i.e. usually contains the full set of capabilities). The default ambient set is set to
 193         <constant>CAP_WAKE_ALARM</constant> for regular users if the PAM session is associated with a local
 194         seat or if it is invoked for the <literal>systemd-user</literal> service. Otherwise defaults to the
 195         empty set.</para>
 196
 197         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 198       </varlistentry>
 199
 200       <varlistentry>
 201         <term><varname>debug</varname><optional>=</optional></term>
 202
 203         <listitem><para>Takes an optional boolean argument. If yes or without the argument, the module will log
 204         debugging information as it operates.</para></listitem>
 205       </varlistentry>
 206     </variablelist>
 207   </refsect1>
 208
 209   <refsect1>
 210     <title>Module Types Provided</title>
 211
 212     <para>Only <option>session</option> is provided.</para>
 213   </refsect1>
 214
 215   <refsect1>
 216     <title>Environment</title>
 217
 218     <para>The following environment variables are initialized by the module and available to the processes of the
 219     user's session:</para>
 220
 221     <variablelist class='environment-variables'>
 222       <varlistentry>
 223         <term><varname>$XDG_SESSION_ID</varname></term>
 224
 225         <listitem><para>A short session identifier, suitable to be used in filenames. The string itself should be
 226         considered opaque, although often it is just the audit session ID as reported by
 227         <filename>/proc/self/sessionid</filename>. Each ID will be assigned only once during machine uptime. It may
 228         hence be used to uniquely label files or other resources of this session. Combine this ID with the boot
 229         identifier, as returned by
 230         <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>, for a
 231         globally unique identifier.</para></listitem>
 232       </varlistentry>
 233
 234       <varlistentry>
 235         <term><varname>$XDG_RUNTIME_DIR</varname></term>
 236
 237         <listitem><para>Path to a user-private user-writable directory
 238         that is bound to the user login time on the machine. It is
 239         automatically created the first time a user logs in and
 240         removed on the user's final logout. If a user logs in twice at
 241         the same time, both sessions will see the same
 242         <varname>$XDG_RUNTIME_DIR</varname> and the same contents. If
 243         a user logs in once, then logs out again, and logs in again,
 244         the directory contents will have been lost in between, but
 245         applications should not rely on this behavior and must be able
 246         to deal with stale files. To store session-private data in
 247         this directory, the user should include the value of
 248         <varname>$XDG_SESSION_ID</varname> in the filename. This
 249         directory shall be used for runtime file system objects such
 250         as <constant>AF_UNIX</constant> sockets, FIFOs, PID files and
 251         similar. It is guaranteed that this directory is local and
 252         offers the greatest possible file system feature set the
 253         operating system provides. For further details, see the <ulink
 254         url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 255         Base Directory Specification</ulink>. <varname>$XDG_RUNTIME_DIR</varname>
 256         is not set if the current user is not the original user of the session.</para></listitem>
 257       </varlistentry>
 258
 259       <varlistentry>
 260         <term><varname>$TZ</varname></term>
 261         <term><varname>$EMAIL</varname></term>
 262         <term><varname>$LANG</varname></term>
 263
 264         <listitem><para>If a JSON user record is known for the user logging in these variables are
 265         initialized from the respective data in the record.</para>
 266
 267         <xi:include href="version-info.xml" xpointer="v245"/></listitem>
 268       </varlistentry>
 269
 270     </variablelist>
 271
 272     <para>The following environment variables are read by the module and may be used by the PAM service to pass
 273     metadata to the module. If these variables are not set when the PAM module is invoked but can be determined
 274     otherwise they are set by the module, so that these variables are initialized for the session and applications if
 275     known at all.</para>
 276
 277     <variablelist class='environment-variables'>
 278       <varlistentry>
 279         <term><varname>$XDG_SESSION_TYPE</varname></term>
 280
 281         <listitem><para>The session type. This may be used instead of <varname>type=</varname> on the module parameter
 282         line, and is usually preferred.</para>
 283
 284         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 285       </varlistentry>
 286
 287       <varlistentry>
 288         <term><varname>$XDG_SESSION_CLASS</varname></term>
 289
 290         <listitem><para>The session class. This may be used instead of <varname>class=</varname> on the module parameter
 291         line, and is usually preferred.</para>
 292
 293         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 294       </varlistentry>
 295
 296       <varlistentry>
 297         <term><varname>$XDG_SESSION_DESKTOP</varname></term>
 298
 299         <listitem><para>The desktop identifier. This may be used instead of <varname>desktop=</varname> on the module
 300         parameter line, and is usually preferred.</para>
 301
 302         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 303       </varlistentry>
 304
 305       <varlistentry>
 306         <term><varname>$XDG_SEAT</varname></term>
 307
 308         <listitem><para>The seat name the session shall be registered
 309         for, if any.</para>
 310
 311         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 312       </varlistentry>
 313
 314       <varlistentry>
 315         <term><varname>$XDG_VTNR</varname></term>
 316
 317         <listitem><para>The VT number the session shall be registered
 318         for, if any. (Only applies to seats with a VT available, such
 319         as <literal>seat0</literal>)</para>
 320
 321         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 322       </varlistentry>
 323     </variablelist>
 324
 325     <para>If not set, <command>pam_systemd</command> will initialize
 326     <varname>$XDG_SEAT</varname> and <varname>$XDG_VTNR</varname>
 327     based on the <varname>$DISPLAY</varname> variable (if the latter is set).</para>
 328   </refsect1>
 329
 330   <refsect1>
 331     <title>Session limits</title>
 332
 333     <para>PAM modules earlier in the stack, that is those that come before <command>pam_systemd.so</command>,
 334     can set session scope limits using the PAM context objects. The data for these objects is provided as <constant>NUL</constant>-terminated C strings
 335     and maps directly to the respective unit resource control directives. Note that these limits apply to individual sessions of the user,
 336     they do not apply to all user processes as a combined whole. In particular, the per-user <command>user@.service</command> unit instance,
 337     which runs the <command>systemd --user</command> manager process and its children, and is tracked outside of any session, being shared
 338     by all the user's sessions, is not covered by these limits.
 339     </para>
 340
 341     <para> See
 342     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information about the resources.
 343     Also, see <citerefentry project='man-pages'><refentrytitle>pam_set_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> for additional information about how to set
 344     the context objects.
 345     </para>
 346
 347     <variablelist class='pam-directives'>
 348       <varlistentry>
 349         <term><varname>systemd.memory_max=</varname></term>
 350
 351         <listitem><para>Sets unit <varname>MemoryMax=</varname>.</para>
 352
 353         <xi:include href="version-info.xml" xpointer="v239"/></listitem>
 354       </varlistentry>
 355
 356       <varlistentry>
 357         <term><varname>systemd.tasks_max=</varname></term>
 358
 359         <listitem><para>Sets unit <varname>TasksMax=</varname>.</para>
 360
 361         <xi:include href="version-info.xml" xpointer="v239"/></listitem>
 362       </varlistentry>
 363
 364       <varlistentry>
 365         <term><varname>systemd.cpu_weight=</varname></term>
 366
 367         <listitem><para>Sets unit <varname>CPUWeight=</varname>.</para>
 368
 369         <xi:include href="version-info.xml" xpointer="v239"/></listitem>
 370       </varlistentry>
 371
 372       <varlistentry>
 373         <term><varname>systemd.io_weight=</varname></term>
 374
 375         <listitem><para>Sets unit <varname>IOWeight=</varname>.</para>
 376
 377         <xi:include href="version-info.xml" xpointer="v239"/></listitem>
 378       </varlistentry>
 379
 380       <varlistentry>
 381         <term><varname>systemd.runtime_max_sec=</varname></term>
 382
 383         <listitem><para>Sets unit <varname>RuntimeMaxSec=</varname>.</para>
 384
 385         <xi:include href="version-info.xml" xpointer="v244"/></listitem>
 386       </varlistentry>
 387     </variablelist>
 388
 389     <para>Example data as can be provided from an another PAM module:
 390       <programlisting>
 391 pam_set_data(handle, "systemd.memory_max", (void *)"200M", cleanup);
 392 pam_set_data(handle, "systemd.tasks_max",  (void *)"50",   cleanup);
 393 pam_set_data(handle, "systemd.cpu_weight", (void *)"100",  cleanup);
 394 pam_set_data(handle, "systemd.io_weight",  (void *)"340",  cleanup);
 395 pam_set_data(handle, "systemd.runtime_max_sec", (void *)"3600", cleanup);
 396       </programlisting>
 397     </para>
 398
 399   </refsect1>
 400
 401   <refsect1>
 402     <title>Example</title>
 403
 404     <para>Here's an example PAM configuration fragment that allows users sessions to be managed by
 405     <filename>systemd-logind.service</filename>:</para>
 406
 407     <programlisting>#%PAM-1.0
 408 auth      sufficient pam_unix.so
 409 -auth     sufficient pam_systemd_home.so
 410 auth      required   pam_deny.so
 411
 412 account   required   pam_nologin.so
 413 -account  sufficient pam_systemd_home.so
 414 account   sufficient pam_unix.so
 415 account   required   pam_permit.so
 416
 417 -password sufficient pam_systemd_home.so
 418 password  sufficient pam_unix.so sha512 shadow try_first_pass
 419 password  required   pam_deny.so
 420
 421 -session  optional   pam_keyinit.so revoke
 422 -session  optional   pam_loginuid.so
 423 -session  optional   pam_systemd_home.so
 424 <command>-session  optional   pam_systemd.so</command>
 425 session   required   pam_unix.so</programlisting>
 426   </refsect1>
 427
 428   <refsect1>
 429     <title>See Also</title>
 430     <para><simplelist type="inline">
 431       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 432       <member><citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 433       <member><citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 434       <member><citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 435       <member><citerefentry><refentrytitle>pam_systemd_home</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 436       <member><citerefentry project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 437       <member><citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 438       <member><citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 439       <member><citerefentry project='man-pages'><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 440       <member><citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 441       <member><citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 442       <member><citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 443     </simplelist></para>
 444   </refsect1>
 445
 446 </refentry>