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ec07c3c80b
This tries to add information about when each option was added. It goes back to version 183. The version info is included from a separate file to allow generating it, which would allow more control on the formatting of the final output.
186 lines
9.1 KiB
XML
186 lines
9.1 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="pam_systemd_home" conditional='ENABLE_PAM_HOME'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>pam_systemd_home</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>pam_systemd_home</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>pam_systemd_home</refname>
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<refpurpose>Authenticate users and mount home directories via <filename>systemd-homed.service</filename>
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</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>pam_systemd_home.so</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>pam_systemd_home</command> ensures that home directories managed by
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<citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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are automatically activated (mounted) on user login, and are deactivated (unmounted) when the last
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session of the user ends. For such users, it also provides authentication (when per-user disk encryption
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is used, the disk encryption key is derived from the authentication credential supplied at login time),
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account management (the <ulink url="https://systemd.io/USER_RECORD/">JSON user record</ulink> embedded in
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the home store contains account details), and implements the updating of the encryption password (which
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is also used for user authentication).</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>The following options are understood:</para>
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<variablelist class='pam-directives'>
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<varlistentry>
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<term><varname>suspend=</varname></term>
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<listitem><para>Takes a boolean argument. If true, the home directory of the user will be suspended
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automatically during system suspend; if false it will remain active. Automatic suspending of the home
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directory improves security substantially as secret key material is automatically removed from memory
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before the system is put to sleep and must be re-acquired (through user re-authentication) when
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coming back from suspend. It is recommended to set this parameter for all PAM applications that have
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support for automatically re-authenticating via PAM on system resume. If multiple sessions of the
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same user are open in parallel the user's home directory will be left unsuspended on system suspend
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as long as at least one of the sessions does not set this parameter to on. Defaults to
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off.</para>
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<para>Note that TTY logins generally do not support re-authentication on system resume.
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Re-authentication on system resume is primarily a concept implementable in graphical environments, in
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the form of lock screens brought up automatically when the system goes to sleep. This means that if a
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user concurrently uses graphical login sessions that implement the required re-authentication
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mechanism and console logins that do not, the home directory is not locked during suspend, due to the
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logic explained above. That said, it is possible to set this field for TTY logins too, ignoring the
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fact that TTY logins actually don't support the re-authentication mechanism. In that case the TTY
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sessions will appear hung until the user logs in on another virtual terminal (regardless if via
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another TTY session or graphically) which will resume the home directory and unblock the original TTY
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session. (Do note that lack of screen locking on TTY sessions means even though the TTY session
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appears hung, keypresses can still be queued into it, and the existing screen contents be read
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without re-authentication; this limitation is unrelated to the home directory management
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<command>pam_systemd_home</command> and <filename>systemd-homed.service</filename> implement.)</para>
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<para>Turning this option on by default is highly recommended for all sessions, but only if the
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service managing these sessions correctly implements the aforementioned re-authentication. Note that
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the re-authentication must take place from a component running outside of the user's context, so that
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it does not require access to the user's home directory for operation. Traditionally, most desktop
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environments do not implement screen locking this way, and need to be updated
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accordingly.</para>
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<para>This setting may also be controlled via the <varname>$SYSTEMD_HOME_SUSPEND</varname>
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environment variable (see below), which <command>pam_systemd_home</command> reads during initialization and sets
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for sessions. If both the environment variable is set and the module parameter specified the latter
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takes precedence.</para>
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<xi:include href="version-info.xml" xpointer="v245"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>debug</varname><optional>=</optional></term>
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<listitem><para>Takes an optional boolean argument. If yes or without the argument, the module will log
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debugging information as it operates.</para>
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<xi:include href="version-info.xml" xpointer="v245"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Module Types Provided</title>
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<para>The module implements all four PAM operations: <option>auth</option> (to allow authentication using
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the encrypted data), <option>account</option> (because users with
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<filename>systemd-homed.service</filename> user accounts are described in a <ulink
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url="https://systemd.io/USER_RECORD/">JSON user record</ulink> and may be configured in more detail than
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in the traditional Linux user database), <option>session</option> (because user sessions must be tracked
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in order to implement automatic release when the last session of the user is gone),
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<option>password</option> (to change the encryption password — also used for user authentication —
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through PAM).</para>
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</refsect1>
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<refsect1>
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<title>Environment</title>
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<para>The following environment variables are initialized by the module and available to the processes of the
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user's session:</para>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_HOME=1</varname></term>
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<listitem><para>Indicates that the user's home directory is managed by <filename>systemd-homed.service</filename>.</para>
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<xi:include href="version-info.xml" xpointer="v245"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>$SYSTEMD_HOME_SUSPEND=</varname></term>
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<listitem><para>Indicates whether the session has been registered with the suspend mechanism enabled
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or disabled (see above). The variable's value is either <literal>0</literal> or
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<literal>1</literal>. Note that the module both reads the variable when initializing, and sets it for
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sessions.</para>
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<xi:include href="version-info.xml" xpointer="v246"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<para>Here's an example PAM configuration fragment that permits users managed by
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<filename>systemd-homed.service</filename> to log in:</para>
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<programlisting>#%PAM-1.0
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auth sufficient pam_unix.so
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<command>-auth sufficient pam_systemd_home.so</command>
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auth required pam_deny.so
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account required pam_nologin.so
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<command>-account sufficient pam_systemd_home.so</command>
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account sufficient pam_unix.so
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account required pam_permit.so
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<command>-password sufficient pam_systemd_home.so</command>
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password sufficient pam_unix.so sha512 shadow try_first_pass use_authtok
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password required pam_deny.so
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-session optional pam_keyinit.so revoke
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-session optional pam_loginuid.so
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<command>-session optional pam_systemd_home.so</command>
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-session optional pam_systemd.so
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session required pam_unix.so</programlisting>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>homed.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>homectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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