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

Provided by: systemd-homed_253.5-1ubuntu6.1_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.

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

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.

       $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.

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 use_authtok
           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/