man/pam_systemd.xml

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   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="pam_systemd" conditional='HAVE_PAM'>
   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 Record</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 <varname>XDG_SESSION_CLASS</varname>
  94         environment variable (see below) takes precedence. One of <literal>user</literal>, <literal>greeter</literal>,
  95         <literal>lock-screen</literal> or <literal>background</literal>. See
  96         <citerefentry><refentrytitle>sd_session_get_class</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
  97         details about the session class.</para></listitem>
  98       </varlistentry>
  99
 100       <varlistentry>
 101         <term><varname>type=</varname></term>
 102
 103         <listitem><para>Takes a string argument which sets the session type. The <varname>XDG_SESSION_TYPE</varname>
 104         environment variable (see below) takes precedence. One of <literal>unspecified</literal>,
 105         <literal>tty</literal>, <literal>x11</literal>, <literal>wayland</literal> or <literal>mir</literal>. See
 106         <citerefentry><refentrytitle>sd_session_get_type</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
 107         details about the session type.</para></listitem>
 108       </varlistentry>
 109
 110       <varlistentry>
 111         <term><varname>desktop=</varname></term>
 112
 113         <listitem><para>Takes a single, short identifier string for the desktop environment. The
 114         <varname>XDG_SESSION_DESKTOP</varname> environment variable (see below) takes precedence. This may be used to
 115         indicate the session desktop used, where this applies and if this information is available. For example:
 116         <literal>GNOME</literal>, or <literal>KDE</literal>. It is recommended to use the same identifiers and
 117         capitalization as for <varname>$XDG_CURRENT_DESKTOP</varname>, as defined by the <ulink
 118         url="http://standards.freedesktop.org/desktop-entry-spec/latest/">Desktop Entry
 119         Specification</ulink>. (However, note that the option only takes a single item, and not a colon-separated list
 120         like <varname>$XDG_CURRENT_DESKTOP</varname>.) See
 121         <citerefentry><refentrytitle>sd_session_get_desktop</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
 122         further details.</para></listitem>
 123       </varlistentry>
 124
 125       <varlistentry>
 126         <term><varname>debug</varname><optional>=</optional></term>
 127
 128         <listitem><para>Takes an optional boolean argument. If yes or without the argument, the module will log
 129         debugging information as it operates.</para></listitem>
 130       </varlistentry>
 131     </variablelist>
 132   </refsect1>
 133
 134   <refsect1>
 135     <title>Module Types Provided</title>
 136
 137     <para>Only <option>session</option> is provided.</para>
 138   </refsect1>
 139
 140   <refsect1>
 141     <title>Environment</title>
 142
 143     <para>The following environment variables are initialized by the module and available to the processes of the
 144     user's session:</para>
 145
 146     <variablelist class='environment-variables'>
 147       <varlistentry>
 148         <term><varname>$XDG_SESSION_ID</varname></term>
 149
 150         <listitem><para>A short session identifier, suitable to be used in filenames. The string itself should be
 151         considered opaque, although often it is just the audit session ID as reported by
 152         <filename>/proc/self/sessionid</filename>. Each ID will be assigned only once during machine uptime. It may
 153         hence be used to uniquely label files or other resources of this session. Combine this ID with the boot
 154         identifier, as returned by
 155         <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>, for a
 156         globally unique identifier.</para></listitem>
 157       </varlistentry>
 158
 159       <varlistentry>
 160         <term><varname>$XDG_RUNTIME_DIR</varname></term>
 161
 162         <listitem><para>Path to a user-private user-writable directory
 163         that is bound to the user login time on the machine. It is
 164         automatically created the first time a user logs in and
 165         removed on the user's final logout. If a user logs in twice at
 166         the same time, both sessions will see the same
 167         <varname>$XDG_RUNTIME_DIR</varname> and the same contents. If
 168         a user logs in once, then logs out again, and logs in again,
 169         the directory contents will have been lost in between, but
 170         applications should not rely on this behavior and must be able
 171         to deal with stale files. To store session-private data in
 172         this directory, the user should include the value of
 173         <varname>$XDG_SESSION_ID</varname> in the filename. This
 174         directory shall be used for runtime file system objects such
 175         as <constant>AF_UNIX</constant> sockets, FIFOs, PID files and
 176         similar. It is guaranteed that this directory is local and
 177         offers the greatest possible file system feature set the
 178         operating system provides. For further details, see the <ulink
 179         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 180         Base Directory Specification</ulink>. <varname>$XDG_RUNTIME_DIR</varname>
 181         is not set if the current user is not the original user of the session.</para></listitem>
 182       </varlistentry>
 183
 184       <varlistentry>
 185         <term><varname>$TZ</varname></term>
 186         <term><varname>$EMAIL</varname></term>
 187         <term><varname>$LANG</varname></term>
 188
 189         <listitem><para>If a JSON user record is known for the user logging in these variables are
 190         initialized from the respective data in the record.</para></listitem>
 191       </varlistentry>
 192
 193     </variablelist>
 194
 195     <para>The following environment variables are read by the module and may be used by the PAM service to pass
 196     metadata to the module. If these variables are not set when the PAM module is invoked but can be determined
 197     otherwise they are set by the module, so that these variables are initialized for the session and applications if
 198     known at all.</para>
 199
 200     <variablelist class='environment-variables'>
 201       <varlistentry>
 202         <term><varname>$XDG_SESSION_TYPE</varname></term>
 203
 204         <listitem><para>The session type. This may be used instead of <varname>type=</varname> on the module parameter
 205         line, and is usually preferred.</para></listitem>
 206       </varlistentry>
 207
 208       <varlistentry>
 209         <term><varname>$XDG_SESSION_CLASS</varname></term>
 210
 211         <listitem><para>The session class. This may be used instead of <varname>class=</varname> on the module parameter
 212         line, and is usually preferred.</para></listitem>
 213       </varlistentry>
 214
 215       <varlistentry>
 216         <term><varname>$XDG_SESSION_DESKTOP</varname></term>
 217
 218         <listitem><para>The desktop identifier. This may be used instead of <varname>desktop=</varname> on the module
 219         parameter line, and is usually preferred.</para></listitem>
 220       </varlistentry>
 221
 222       <varlistentry>
 223         <term><varname>$XDG_SEAT</varname></term>
 224
 225         <listitem><para>The seat name the session shall be registered
 226         for, if any.</para></listitem>
 227       </varlistentry>
 228
 229       <varlistentry>
 230         <term><varname>$XDG_VTNR</varname></term>
 231
 232         <listitem><para>The VT number the session shall be registered
 233         for, if any. (Only applies to seats with a VT available, such
 234         as <literal>seat0</literal>)</para></listitem>
 235       </varlistentry>
 236     </variablelist>
 237
 238     <para>If not set, <command>pam_systemd</command> will initialize
 239     <varname>$XDG_SEAT</varname> and <varname>$XDG_VTNR</varname>
 240     based on the <varname>$DISPLAY</varname> variable (if the latter is set).</para>
 241   </refsect1>
 242
 243   <refsect1>
 244     <title>Session limits</title>
 245
 246     <para>PAM modules earlier in the stack, that is those that come before <command>pam_systemd.so</command>,
 247     can set session scope limits using the PAM context objects. The data for these objects is provided as NUL-terminated C strings
 248     and maps directly to the respective unit resource control directives. Note that these limits apply to individual sessions of the user,
 249     they do not apply to all user processes as a combined whole. In particular, the per-user <command>user@.service</command> unit instance,
 250     which runs the <command>systemd --user</command> manager process and its children, and is tracked outside of any session, being shared
 251     by all the user's sessions, is not covered by these limits.
 252     </para>
 253
 254     <para> See
 255     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information about the resources.
 256     Also, see <citerefentry project='man-pages'><refentrytitle>pam_set_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> for additional information about how to set
 257     the context objects.
 258     </para>
 259
 260     <variablelist class='pam-directives'>
 261       <varlistentry>
 262         <term><varname>systemd.memory_max=</varname></term>
 263
 264         <listitem><para>Sets unit <varname>MemoryMax=</varname>.</para></listitem>
 265       </varlistentry>
 266
 267       <varlistentry>
 268         <term><varname>systemd.tasks_max=</varname></term>
 269
 270         <listitem><para>Sets unit <varname>TasksMax=</varname>.</para></listitem>
 271       </varlistentry>
 272
 273       <varlistentry>
 274         <term><varname>systemd.cpu_weight=</varname></term>
 275
 276         <listitem><para>Sets unit <varname>CPUWeight=</varname>.</para></listitem>
 277       </varlistentry>
 278
 279       <varlistentry>
 280         <term><varname>systemd.io_weight=</varname></term>
 281
 282         <listitem><para>Sets unit <varname>IOWeight=</varname>.</para></listitem>
 283       </varlistentry>
 284
 285       <varlistentry>
 286         <term><varname>systemd.runtime_max_sec=</varname></term>
 287
 288         <listitem><para>Sets unit <varname>RuntimeMaxSec=</varname>.</para></listitem>
 289       </varlistentry>
 290     </variablelist>
 291
 292     <para>Example data as can be provided from an another PAM module:
 293       <programlisting>
 294 pam_set_data(handle, "systemd.memory_max", (void *)"200M", cleanup);
 295 pam_set_data(handle, "systemd.tasks_max",  (void *)"50",   cleanup);
 296 pam_set_data(handle, "systemd.cpu_weight", (void *)"100",  cleanup);
 297 pam_set_data(handle, "systemd.io_weight",  (void *)"340",  cleanup);
 298 pam_set_data(handle, "systemd.runtime_max_sec", (void *)"3600", cleanup);
 299       </programlisting>
 300     </para>
 301
 302   </refsect1>
 303
 304   <refsect1>
 305     <title>Example</title>
 306
 307     <para>Here's an example PAM configuration fragment that allows users sessions to be managed by
 308     <filename>systemd-logind.service</filename>:</para>
 309
 310     <programlisting>#%PAM-1.0
 311 auth      sufficient pam_unix.so
 312 -auth     sufficient pam_systemd_home.so
 313 auth      required   pam_deny.so
 314
 315 account   required   pam_nologin.so
 316 -account  sufficient pam_systemd_home.so
 317 account   sufficient pam_unix.so
 318 account   required   pam_permit.so
 319
 320 -password sufficient pam_systemd_home.so
 321 password  sufficient pam_unix.so sha512 shadow try_first_pass try_authtok
 322 password  required   pam_deny.so
 323
 324 -session  optional   pam_keyinit.so revoke
 325 -session  optional   pam_loginuid.so
 326 -session  optional   pam_systemd_home.so
 327 <command>-session  optional   pam_systemd.so</command>
 328 session   required   pam_unix.so</programlisting>
 329   </refsect1>
 330
 331   <refsect1>
 332     <title>See Also</title>
 333     <para>
 334       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 335       <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 336       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 337       <citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 338       <citerefentry><refentrytitle>pam_systemd_home</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 339       <citerefentry project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 340       <citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 341       <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 342       <citerefentry project='man-pages'><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 343       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 344       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 345       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 346     </para>
 347   </refsect1>
 348
 349 </refentry>