man/pam_systemd.xml

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   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 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 <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>$XDG_CURRENT_DESKTOP</varname>, as defined by the <ulink
 118         url="https://standards.freedesktop.org/desktop-entry-spec/latest/">Desktop Entry
 119         Specification</ulink>. (However, note that the option only takes a single item, and not a colon-separated list
 120         like <varname>$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>default-capability-bounding-set=</varname></term>
 127         <term><varname>default-capability-ambient-set=</varname></term>
 128
 129         <listitem><para>Takes a comma-separated list of process capabilities
 130         (e.g. <constant>CAP_WAKE_ALARM</constant>, <constant>CAP_BLOCK_SUSPEND</constant>, …) to set for the
 131         invoked session's processes, if the user record does not encode appropriate sets of capabilities
 132         directly. See <citerefentry
 133         project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 134         for details on the capabilities concept. If not specified, the default bounding set is left as is
 135         (i.e. usually contains the full set of capabilities). The default ambient set is set to
 136         <constant>CAP_WAKE_ALARM</constant> for regular users if the PAM session is associated with a local
 137         seat or if it is invoked for the <literal>systemd-user</literal> service. Otherwise defaults to the
 138         empty set.</para></listitem>
 139       </varlistentry>
 140
 141       <varlistentry>
 142         <term><varname>debug</varname><optional>=</optional></term>
 143
 144         <listitem><para>Takes an optional boolean argument. If yes or without the argument, the module will log
 145         debugging information as it operates.</para></listitem>
 146       </varlistentry>
 147     </variablelist>
 148   </refsect1>
 149
 150   <refsect1>
 151     <title>Module Types Provided</title>
 152
 153     <para>Only <option>session</option> is provided.</para>
 154   </refsect1>
 155
 156   <refsect1>
 157     <title>Environment</title>
 158
 159     <para>The following environment variables are initialized by the module and available to the processes of the
 160     user's session:</para>
 161
 162     <variablelist class='environment-variables'>
 163       <varlistentry>
 164         <term><varname>$XDG_SESSION_ID</varname></term>
 165
 166         <listitem><para>A short session identifier, suitable to be used in filenames. The string itself should be
 167         considered opaque, although often it is just the audit session ID as reported by
 168         <filename>/proc/self/sessionid</filename>. Each ID will be assigned only once during machine uptime. It may
 169         hence be used to uniquely label files or other resources of this session. Combine this ID with the boot
 170         identifier, as returned by
 171         <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>, for a
 172         globally unique identifier.</para></listitem>
 173       </varlistentry>
 174
 175       <varlistentry>
 176         <term><varname>$XDG_RUNTIME_DIR</varname></term>
 177
 178         <listitem><para>Path to a user-private user-writable directory
 179         that is bound to the user login time on the machine. It is
 180         automatically created the first time a user logs in and
 181         removed on the user's final logout. If a user logs in twice at
 182         the same time, both sessions will see the same
 183         <varname>$XDG_RUNTIME_DIR</varname> and the same contents. If
 184         a user logs in once, then logs out again, and logs in again,
 185         the directory contents will have been lost in between, but
 186         applications should not rely on this behavior and must be able
 187         to deal with stale files. To store session-private data in
 188         this directory, the user should include the value of
 189         <varname>$XDG_SESSION_ID</varname> in the filename. This
 190         directory shall be used for runtime file system objects such
 191         as <constant>AF_UNIX</constant> sockets, FIFOs, PID files and
 192         similar. It is guaranteed that this directory is local and
 193         offers the greatest possible file system feature set the
 194         operating system provides. For further details, see the <ulink
 195         url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 196         Base Directory Specification</ulink>. <varname>$XDG_RUNTIME_DIR</varname>
 197         is not set if the current user is not the original user of the session.</para></listitem>
 198       </varlistentry>
 199
 200       <varlistentry>
 201         <term><varname>$TZ</varname></term>
 202         <term><varname>$EMAIL</varname></term>
 203         <term><varname>$LANG</varname></term>
 204
 205         <listitem><para>If a JSON user record is known for the user logging in these variables are
 206         initialized from the respective data in the record.</para></listitem>
 207       </varlistentry>
 208
 209     </variablelist>
 210
 211     <para>The following environment variables are read by the module and may be used by the PAM service to pass
 212     metadata to the module. If these variables are not set when the PAM module is invoked but can be determined
 213     otherwise they are set by the module, so that these variables are initialized for the session and applications if
 214     known at all.</para>
 215
 216     <variablelist class='environment-variables'>
 217       <varlistentry>
 218         <term><varname>$XDG_SESSION_TYPE</varname></term>
 219
 220         <listitem><para>The session type. This may be used instead of <varname>type=</varname> on the module parameter
 221         line, and is usually preferred.</para></listitem>
 222       </varlistentry>
 223
 224       <varlistentry>
 225         <term><varname>$XDG_SESSION_CLASS</varname></term>
 226
 227         <listitem><para>The session class. This may be used instead of <varname>class=</varname> on the module parameter
 228         line, and is usually preferred.</para></listitem>
 229       </varlistentry>
 230
 231       <varlistentry>
 232         <term><varname>$XDG_SESSION_DESKTOP</varname></term>
 233
 234         <listitem><para>The desktop identifier. This may be used instead of <varname>desktop=</varname> on the module
 235         parameter line, and is usually preferred.</para></listitem>
 236       </varlistentry>
 237
 238       <varlistentry>
 239         <term><varname>$XDG_SEAT</varname></term>
 240
 241         <listitem><para>The seat name the session shall be registered
 242         for, if any.</para></listitem>
 243       </varlistentry>
 244
 245       <varlistentry>
 246         <term><varname>$XDG_VTNR</varname></term>
 247
 248         <listitem><para>The VT number the session shall be registered
 249         for, if any. (Only applies to seats with a VT available, such
 250         as <literal>seat0</literal>)</para></listitem>
 251       </varlistentry>
 252     </variablelist>
 253
 254     <para>If not set, <command>pam_systemd</command> will initialize
 255     <varname>$XDG_SEAT</varname> and <varname>$XDG_VTNR</varname>
 256     based on the <varname>$DISPLAY</varname> variable (if the latter is set).</para>
 257   </refsect1>
 258
 259   <refsect1>
 260     <title>Session limits</title>
 261
 262     <para>PAM modules earlier in the stack, that is those that come before <command>pam_systemd.so</command>,
 263     can set session scope limits using the PAM context objects. The data for these objects is provided as <constant>NUL</constant>-terminated C strings
 264     and maps directly to the respective unit resource control directives. Note that these limits apply to individual sessions of the user,
 265     they do not apply to all user processes as a combined whole. In particular, the per-user <command>user@.service</command> unit instance,
 266     which runs the <command>systemd --user</command> manager process and its children, and is tracked outside of any session, being shared
 267     by all the user's sessions, is not covered by these limits.
 268     </para>
 269
 270     <para> See
 271     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information about the resources.
 272     Also, see <citerefentry project='man-pages'><refentrytitle>pam_set_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> for additional information about how to set
 273     the context objects.
 274     </para>
 275
 276     <variablelist class='pam-directives'>
 277       <varlistentry>
 278         <term><varname>systemd.memory_max=</varname></term>
 279
 280         <listitem><para>Sets unit <varname>MemoryMax=</varname>.</para></listitem>
 281       </varlistentry>
 282
 283       <varlistentry>
 284         <term><varname>systemd.tasks_max=</varname></term>
 285
 286         <listitem><para>Sets unit <varname>TasksMax=</varname>.</para></listitem>
 287       </varlistentry>
 288
 289       <varlistentry>
 290         <term><varname>systemd.cpu_weight=</varname></term>
 291
 292         <listitem><para>Sets unit <varname>CPUWeight=</varname>.</para></listitem>
 293       </varlistentry>
 294
 295       <varlistentry>
 296         <term><varname>systemd.io_weight=</varname></term>
 297
 298         <listitem><para>Sets unit <varname>IOWeight=</varname>.</para></listitem>
 299       </varlistentry>
 300
 301       <varlistentry>
 302         <term><varname>systemd.runtime_max_sec=</varname></term>
 303
 304         <listitem><para>Sets unit <varname>RuntimeMaxSec=</varname>.</para></listitem>
 305       </varlistentry>
 306     </variablelist>
 307
 308     <para>Example data as can be provided from an another PAM module:
 309       <programlisting>
 310 pam_set_data(handle, "systemd.memory_max", (void *)"200M", cleanup);
 311 pam_set_data(handle, "systemd.tasks_max",  (void *)"50",   cleanup);
 312 pam_set_data(handle, "systemd.cpu_weight", (void *)"100",  cleanup);
 313 pam_set_data(handle, "systemd.io_weight",  (void *)"340",  cleanup);
 314 pam_set_data(handle, "systemd.runtime_max_sec", (void *)"3600", cleanup);
 315       </programlisting>
 316     </para>
 317
 318   </refsect1>
 319
 320   <refsect1>
 321     <title>Example</title>
 322
 323     <para>Here's an example PAM configuration fragment that allows users sessions to be managed by
 324     <filename>systemd-logind.service</filename>:</para>
 325
 326     <programlisting>#%PAM-1.0
 327 auth      sufficient pam_unix.so
 328 -auth     sufficient pam_systemd_home.so
 329 auth      required   pam_deny.so
 330
 331 account   required   pam_nologin.so
 332 -account  sufficient pam_systemd_home.so
 333 account   sufficient pam_unix.so
 334 account   required   pam_permit.so
 335
 336 -password sufficient pam_systemd_home.so
 337 password  sufficient pam_unix.so sha512 shadow try_first_pass use_authtok
 338
 339 password  required   pam_deny.so
 340
 341 -session  optional   pam_keyinit.so revoke
 342 -session  optional   pam_loginuid.so
 343 -session  optional   pam_systemd_home.so
 344 <command>-session  optional   pam_systemd.so</command>
 345 session   required   pam_unix.so</programlisting>
 346   </refsect1>
 347
 348   <refsect1>
 349     <title>See Also</title>
 350     <para>
 351       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 352       <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 353       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 354       <citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 355       <citerefentry><refentrytitle>pam_systemd_home</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 356       <citerefentry project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 357       <citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 358       <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 359       <citerefentry project='man-pages'><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 360       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 361       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 362       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 363     </para>
 364   </refsect1>
 365
 366 </refentry>