Ubuntu Manpage: pam_systemd_home - Authenticate users and mount home directories via systemd-homed.service

Provided by: systemd-homed_255.4-1ubuntu8.5_amd64

NAME

       pam_systemd_home - Authenticate users and mount home directories via systemd-homed.service

SYNOPSIS

       pam_systemd_home.so

DESCRIPTION

       pam_systemd_home ensures that home directories managed by systemd-homed.service(8) are automatically
       activated (mounted) on user login, and are deactivated (unmounted) when the last session of the user
       ends. For such users, it also provides authentication (when per-user disk encryption is used, the disk
       encryption key is derived from the authentication credential supplied at login time), account management
       (the JSON user record[1] embedded in the home store contains account details), and implements the
       updating of the encryption password (which is also used for user authentication).

OPTIONS

The following options are understood:

suspend=
Takes a boolean argument. If true, the home directory of the user will be suspended automatically
during system suspend; if false it will remain active. Automatic suspending of the home directory
improves security substantially as secret key material is automatically removed from memory before
the system is put to sleep and must be re-acquired (through user re-authentication) when coming back
from suspend. It is recommended to set this parameter for all PAM applications that have support for
automatically re-authenticating via PAM on system resume. If multiple sessions of the same user are
open in parallel the user's home directory will be left unsuspended on system suspend as long as at
least one of the sessions does not set this parameter to on. Defaults to off.

Note that TTY logins generally do not support re-authentication on system resume. Re-authentication
on system resume is primarily a concept implementable in graphical environments, in the form of lock
screens brought up automatically when the system goes to sleep. This means that if a user
concurrently uses graphical login sessions that implement the required re-authentication mechanism
and console logins that do not, the home directory is not locked during suspend, due to the logic
explained above. That said, it is possible to set this field for TTY logins too, ignoring the fact
that TTY logins actually don't support the re-authentication mechanism. In that case the TTY sessions
will appear hung until the user logs in on another virtual terminal (regardless if via another TTY
session or graphically) which will resume the home directory and unblock the original TTY session.
(Do note that lack of screen locking on TTY sessions means even though the TTY session appears hung,
keypresses can still be queued into it, and the existing screen contents be read without
re-authentication; this limitation is unrelated to the home directory management pam_systemd_home and
systemd-homed.service implement.)

Turning this option on by default is highly recommended for all sessions, but only if the service
managing these sessions correctly implements the aforementioned re-authentication. Note that the
re-authentication must take place from a component running outside of the user's context, so that it
does not require access to the user's home directory for operation. Traditionally, most desktop
environments do not implement screen locking this way, and need to be updated accordingly.

This setting may also be controlled via the $SYSTEMD_HOME_SUSPEND environment variable (see below),
which pam_systemd_home reads during initialization and sets for sessions. If both the environment
variable is set and the module parameter specified the latter takes precedence.

Added in version 245.

debug[=]
Takes an optional boolean argument. If yes or without the argument, the module will log debugging
information as it operates.

Added in version 245.

MODULE TYPES PROVIDED

       The module implements all four PAM operations: auth (to allow authentication using the encrypted data),
       account (because users with systemd-homed.service user accounts are described in a JSON user record[1]
       and may be configured in more detail than in the traditional Linux user database), session (because user
       sessions must be tracked in order to implement automatic release when the last session of the user is
       gone), password (to change the encryption password — also used for user authentication — through PAM).

ENVIRONMENT

       The following environment variables are initialized by the module and available to the processes of the
       user's session:

       $SYSTEMD_HOME=1
           Indicates that the user's home directory is managed by systemd-homed.service.

           Added in version 245.

       $SYSTEMD_HOME_SUSPEND=
           Indicates whether the session has been registered with the suspend mechanism enabled or disabled (see
           above). The variable's value is either "0" or "1". Note that the module both reads the variable when
           initializing, and sets it for sessions.

           Added in version 246.

EXAMPLE

       Here's an example PAM configuration fragment that permits users managed by systemd-homed.service to log
       in:

           #%PAM-1.0
           auth      sufficient pam_unix.so
           -auth     sufficient pam_systemd_home.so
           auth      required   pam_deny.so

           account   required   pam_nologin.so
           -account  sufficient pam_systemd_home.so
           account   sufficient pam_unix.so
           account   required   pam_permit.so

           -password sufficient pam_systemd_home.so
           password  sufficient pam_unix.so sha512 shadow try_first_pass
           password  required   pam_deny.so

           -session  optional   pam_keyinit.so revoke
           -session  optional   pam_loginuid.so
           -session  optional   pam_systemd_home.so
           -session  optional   pam_systemd.so
           session   required   pam_unix.so

NOTES

        1. JSON user record
           https://systemd.io/USER_RECORD/