man/pam_systemd_home.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="pam_systemd_home" conditional='ENABLE_PAM_HOME'
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>pam_systemd_home</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>pam_systemd_home</refentrytitle>
  16     <manvolnum>8</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>pam_systemd_home</refname>
  21     <refpurpose>Authenticate users and mount home directories via <filename>systemd-homed.service</filename>
  22     </refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para><filename>pam_systemd_home.so</filename></para>
  27   </refsynopsisdiv>
  28
  29   <refsect1>
  30     <title>Description</title>
  31
  32     <para><command>pam_systemd_home</command> ensures that home directories managed by
  33     <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  34     are automatically activated (mounted) on user login, and are deactivated (unmounted) when the last
  35     session of the user ends. For such users, it also provides authentication (when per-user disk encryption
  36     is used, the disk encryption key is derived from the authentication credential supplied at login time),
  37     account management (the <ulink url="https://systemd.io/USER_RECORD/">JSON user record</ulink> embedded in
  38     the home store contains account details), and implements the updating of the encryption password (which
  39     is also used for user authentication).</para>
  40   </refsect1>
  41
  42   <refsect1>
  43     <title>Options</title>
  44
  45     <para>The following options are understood:</para>
  46
  47     <variablelist class='pam-directives'>
  48
  49       <varlistentry>
  50         <term><varname>suspend=</varname></term>
  51
  52         <listitem><para>Takes a boolean argument. If true, the home directory of the user will be suspended
  53         automatically during system suspend; if false it will remain active. Automatic suspending of the home
  54         directory improves security substantially as secret key material is automatically removed from memory
  55         before the system is put to sleep and must be re-acquired (through user re-authentication) when
  56         coming back from suspend. It is recommended to set this parameter for all PAM applications that have
  57         support for automatically re-authenticating via PAM on system resume. If multiple sessions of the
  58         same user are open in parallel the user's home directory will be left unsuspended on system suspend
  59         as long as at least one of the sessions does not set this parameter to on. Defaults to
  60         off.</para>
  61
  62         <para>Note that TTY logins generally do not support re-authentication on system resume.
  63         Re-authentication on system resume is primarily a concept implementable in graphical environments, in
  64         the form of lock screens brought up automatically when the system goes to sleep. This means that if a
  65         user concurrently uses graphical login sessions that implement the required re-authentication
  66         mechanism and console logins that do not, the home directory is not locked during suspend, due to the
  67         logic explained above. That said, it is possible to set this field for TTY logins too, ignoring the
  68         fact that TTY logins actually don't support the re-authentication mechanism. In that case the TTY
  69         sessions will appear hung until the user logs in on another virtual terminal (regardless if via
  70         another TTY session or graphically) which will resume the home directory and unblock the original TTY
  71         session. (Do note that lack of screen locking on TTY sessions means even though the TTY session
  72         appears hung, keypresses can still be queued into it, and the existing screen contents be read
  73         without re-authentication; this limitation is unrelated to the home directory management
  74         <command>pam_systemd_home</command> and <filename>systemd-homed.service</filename> implement.)</para>
  75
  76         <para>Turning this option on by default is highly recommended for all sessions, but only if the
  77         service managing these sessions correctly implements the aforementioned re-authentication. Note that
  78         the re-authentication must take place from a component running outside of the user's context, so that
  79         it does not require access to the user's home directory for operation. Traditionally, most desktop
  80         environments do not implement screen locking this way, and need to be updated
  81         accordingly.</para>
  82
  83         <para>This setting may also be controlled via the <varname>$SYSTEMD_HOME_SUSPEND</varname>
  84         environment variable (see below), which <command>pam_systemd_home</command> reads during initialization and sets
  85         for sessions. If both the environment variable is set and the module parameter specified the latter
  86         takes precedence.</para>
  87
  88         <xi:include href="version-info.xml" xpointer="v245"/></listitem>
  89       </varlistentry>
  90
  91       <varlistentry>
  92         <term><varname>debug</varname><optional>=</optional></term>
  93
  94         <listitem><para>Takes an optional boolean argument. If yes or without the argument, the module will log
  95         debugging information as it operates.</para>
  96
  97         <xi:include href="version-info.xml" xpointer="v245"/></listitem>
  98       </varlistentry>
  99     </variablelist>
 100   </refsect1>
 101
 102   <refsect1>
 103     <title>Module Types Provided</title>
 104
 105     <para>The module implements all four PAM operations: <option>auth</option> (to allow authentication using
 106     the encrypted data), <option>account</option> (because users with
 107     <filename>systemd-homed.service</filename> user accounts are described in a <ulink
 108     url="https://systemd.io/USER_RECORD/">JSON user record</ulink> and may be configured in more detail than
 109     in the traditional Linux user database), <option>session</option> (because user sessions must be tracked
 110     in order to implement automatic release when the last session of the user is gone),
 111     <option>password</option> (to change the encryption password — also used for user authentication —
 112     through PAM).</para>
 113   </refsect1>
 114
 115   <refsect1>
 116     <title>Environment</title>
 117
 118     <para>The following environment variables are initialized by the module and available to the processes of the
 119     user's session:</para>
 120
 121     <variablelist class='environment-variables'>
 122       <varlistentry>
 123         <term><varname>$SYSTEMD_HOME=1</varname></term>
 124
 125         <listitem><para>Indicates that the user's home directory is managed by <filename>systemd-homed.service</filename>.</para>
 126
 127         <xi:include href="version-info.xml" xpointer="v245"/></listitem>
 128       </varlistentry>
 129
 130       <varlistentry>
 131         <term><varname>$SYSTEMD_HOME_SUSPEND=</varname></term>
 132
 133         <listitem><para>Indicates whether the session has been registered with the suspend mechanism enabled
 134         or disabled (see above). The variable's value is either <literal>0</literal> or
 135         <literal>1</literal>. Note that the module both reads the variable when initializing, and sets it for
 136         sessions.</para>
 137
 138         <xi:include href="version-info.xml" xpointer="v246"/></listitem>
 139       </varlistentry>
 140
 141     </variablelist>
 142   </refsect1>
 143
 144   <refsect1>
 145     <title>Example</title>
 146
 147     <para>Here's an example PAM configuration fragment that permits users managed by
 148     <filename>systemd-homed.service</filename> to log in:</para>
 149
 150     <programlisting>#%PAM-1.0
 151 auth      sufficient pam_unix.so
 152 <command>-auth     sufficient pam_systemd_home.so</command>
 153 auth      required   pam_deny.so
 154
 155 account   required   pam_nologin.so
 156 <command>-account  sufficient pam_systemd_home.so</command>
 157 account   sufficient pam_unix.so
 158 account   required   pam_permit.so
 159
 160 <command>-password sufficient pam_systemd_home.so</command>
 161 password  sufficient pam_unix.so sha512 shadow try_first_pass
 162 password  required   pam_deny.so
 163
 164 -session  optional   pam_keyinit.so revoke
 165 -session  optional   pam_loginuid.so
 166 <command>-session  optional   pam_systemd_home.so</command>
 167 -session  optional   pam_systemd.so
 168 session   required   pam_unix.so</programlisting>
 169   </refsect1>
 170
 171   <refsect1>
 172     <title>See Also</title>
 173     <para><simplelist type="inline">
 174       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 175       <member><citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 176       <member><citerefentry><refentrytitle>homed.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 177       <member><citerefentry><refentrytitle>homectl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 178       <member><citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 179       <member><citerefentry project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 180       <member><citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 181       <member><citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 182     </simplelist></para>
 183   </refsect1>
 184
 185 </refentry>