Provided by: libpam-systemd_245.4-4ubuntu3_amd64 bug


       pam_systemd - Register user sessions in the systemd login manager



       pam_systemd registers user sessions with the systemd login manager systemd-
       logind.service(8), and hence the systemd control group hierarchy.

       The module also applies various resource management and runtime parameters to the new
       session, as configured in the JSON User Record[1] of the user, when one is defined.

       On login, this module — in conjunction with systemd-logind.service — ensures the

        1. If it does not exist yet, the user runtime directory /run/user/$UID is either created
           or mounted as new "tmpfs" file system with quota applied, and its ownership changed to
           the user that is logging in.

        2. The $XDG_SESSION_ID environment variable is initialized. If auditing is available and
  was run before this module (which is highly recommended), the variable
           is initialized from the auditing session id (/proc/self/sessionid). Otherwise, an
           independent session counter is used.

        3. A new systemd scope unit is created for the session. If this is the first concurrent
           session of the user, an implicit per-user slice unit below user.slice is automatically
           created and the scope placed into it. An instance of the system service user@.service,
           which runs the systemd user manager instance, is started.

        4. The "$TZ", "$EMAIL" and "$LANG" environment variables are configured for the user,
           based on the respective data from the user's JSON record (if it is defined). Moreover,
           any environment variables explicitly configured in the user record are imported, and
           the umask, nice level, and resource limits initialized.

       On logout, this module ensures the following:

        1. If enabled in logind.conf(5) (KillUserProcesses=), all processes of the session are
           terminated. If the last concurrent session of a user ends, the user's systemd instance
           will be terminated too, and so will the user's slice unit.

        2. If the last concurrent session of a user ends, the user runtime directory
           /run/user/$UID and all its contents are removed, too.

       If the system was not booted up with systemd as init system, this module does nothing and
       immediately returns PAM_SUCCESS.


       The following options are understood:

           Takes a string argument which sets the session class. The XDG_SESSION_CLASS
           environment variable (see below) takes precedence. One of "user", "greeter",
           "lock-screen" or "background". See sd_session_get_class(3) for details about the
           session class.

           Takes a string argument which sets the session type. The XDG_SESSION_TYPE environment
           variable (see below) takes precedence. One of "unspecified", "tty", "x11", "wayland"
           or "mir". See sd_session_get_type(3) for details about the session type.

           Takes a single, short identifier string for the desktop environment. The
           XDG_SESSION_DESKTOP environment variable (see below) takes precedence. This may be
           used to indicate the session desktop used, where this applies and if this information
           is available. For example: "GNOME", or "KDE". It is recommended to use the same
           identifiers and capitalization as for $XDG_CURRENT_DESKTOP, as defined by the Desktop
           Entry Specification[2]. (However, note that the option only takes a single item, and
           not a colon-separated list like $XDG_CURRENT_DESKTOP.) See sd_session_get_desktop(3)
           for further details.

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


       Only session is provided.


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

           A short session identifier, suitable to be used in filenames. The string itself should
           be considered opaque, although often it is just the audit session ID as reported by
           /proc/self/sessionid. Each ID will be assigned only once during machine uptime. It may
           hence be used to uniquely label files or other resources of this session. Combine this
           ID with the boot identifier, as returned by sd_id128_get_boot(3), for a globally
           unique identifier for the current session.

           Path to a user-private user-writable directory that is bound to the user login time on
           the machine. It is automatically created the first time a user logs in and removed on
           the user's final logout. If a user logs in twice at the same time, both sessions will
           see the same $XDG_RUNTIME_DIR and the same contents. If a user logs in once, then logs
           out again, and logs in again, the directory contents will have been lost in between,
           but applications should not rely on this behavior and must be able to deal with stale
           files. To store session-private data in this directory, the user should include the
           value of $XDG_SESSION_ID in the filename. This directory shall be used for runtime
           file system objects such as AF_UNIX sockets, FIFOs, PID files and similar. It is
           guaranteed that this directory is local and offers the greatest possible file system
           feature set the operating system provides. For further details, see the XDG Base
           Directory Specification[3].  $XDG_RUNTIME_DIR is not set if the current user is not
           the original user of the session.

       $TZ, $EMAIL, $LANG
           If a JSON user record is known for the user logging in these variables are initialized
           from the respective data in the record.

       The following environment variables are read by the module and may be used by the PAM
       service to pass metadata to the module. If these variables are not set when the PAM module
       is invoked but can be determined otherwise they are set by the module, so that these
       variables are initialized for the session and applications if known at all.

           The session type. This may be used instead of type= on the module parameter line, and
           is usually preferred.

           The session class. This may be used instead of class= on the module parameter line,
           and is usually preferred.

           The desktop identifier. This may be used instead of desktop= on the module parameter
           line, and is usually preferred.

           The seat name the session shall be registered for, if any.

           The VT number the session shall be registered for, if any. (Only applies to seats with
           a VT available, such as "seat0")

       If not set, pam_systemd will initialize $XDG_SEAT and $XDG_VTNR based on the $DISPLAY
       variable (if the latter is set).


       PAM modules earlier in the stack, that is those that come before, can set
       session scope limits using the PAM context objects. The data for these objects is provided
       as NUL-terminated C strings and maps directly to the respective unit resource control
       directives. Note that these limits apply to individual sessions of the user, they do not
       apply to all user processes as a combined whole. In particular, the per-user user@.service
       unit instance, which runs the systemd --user manager process and its children, and is
       tracked outside of any session, being shared by all the user's sessions, is not covered by
       these limits.

       See systemd.resource-control(5) for more information about the resources. Also, see
       pam_set_data(3) for additional information about how to set the context objects.

           Sets unit MemoryMax=.

           Sets unit TasksMax=.

           Sets unit CPUWeight=.

           Sets unit IOWeight=.

           Sets unit RuntimeMaxSec=.

       Example data as can be provided from an another PAM module:

           pam_set_data(handle, "systemd.memory_max", (void *)"200M", cleanup);
           pam_set_data(handle, "systemd.tasks_max",  (void *)"50",   cleanup);
           pam_set_data(handle, "systemd.cpu_weight", (void *)"100",  cleanup);
           pam_set_data(handle, "systemd.io_weight",  (void *)"340",  cleanup);
           pam_set_data(handle, "systemd.runtime_max_sec", (void *)"3600", cleanup);


       Here's an example PAM configuration fragment that allows users sessions to be managed by

           auth     sufficient
           auth     required

           account  required
           account  sufficient
           account  required

           password sufficient sha512 shadow try_first_pass try_authtok
           password required

           -session optional
           -session optional
           session  required


       systemd(1), systemd-logind.service(8), logind.conf(5), loginctl(1), pam_systemd_home(8),
       pam.conf(5), pam.d(5), pam(8), pam_loginuid(8), systemd.scope(5), systemd.slice(5),


        1. JSON User Record

        2. Desktop Entry Specification

        3. XDG Base Directory Specification