pam_systemd

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 pam_loginuid.so 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.

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.

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

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

A 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.

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[1]. $XDG_RUNTIME_DIR is not set if the current user is not the original user of the session.

The session type. This may be used instead of session= 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.

A single, short identifier string for the desktop environment. 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 $XDG_SESSION_DESKTOP only takes a single item, and not a colon-separated list like $XDG_CURRENT_DESKTOP.) See sd_session_get_desktop(3) for more details.

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")

#%PAM-1.0
auth       required     pam_unix.so
auth       required     pam_nologin.so
account    required     pam_unix.so
password   required     pam_unix.so
session    required     pam_unix.so
session    required     pam_loginuid.so
session    required     pam_systemd.so

http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

http://standards.freedesktop.org/desktop-entry-spec/latest/