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 .
On login, this module in conjunction with systemd -logind .service ensures the following:
" 1." 4.2 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 . '-04' 2. '+01' .sp -1
" 2." 4.2 The $XDG_SESSION_ID environment variable is initialized . If auditing is available and pam_loginuid.so was run before this module (which is highly recommended), the variable is initialized from the auditing session id (/proc/self/sessionid) . Otherwise, an independent session counter is used . '-04' 3. '+01' .sp -1
" 3." 4.2 A new systemd scope unit is created for the session . If this is the first concurrent session of the user, an implicit per -user slice unit below user .slice is automatically created and the scope placed into it . An instance of the system service user@ .service, which runs the systemd user manager instance, is started .
On logout, this module ensures the following: '-04' 1. '+01' .sp -1
" 1." 4.2 If enabled in logind.conf (5) ( KillUserProcesses= ),all processes of the session are terminated . If the last concurrent session of a user ends, the user (Aqs systemd instance will be terminated too, and so will the user (Aqs slice unit . '-04' 2. '+01' .sp -1
" 2." 4.2 If the last concurrent session of a user ends, the user runtime directory /run/user/$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:
class= 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 .
type= 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 .
desktop= 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 DesktopEntry Specification  . (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 .
debug [=] 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 (Aqs session:
$XDG_SESSION_ID 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 .
$XDG_RUNTIME_DIR 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 (Aqs 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 XDGBase Directory Specification  . $XDG_RUNTIME_DIR is not set if the current user is not the original user of the session .
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 .
$XDG_SESSION_TYPE The session type . This may be used instead of session= on the module parameter line, and is usually preferred .
$XDG_SESSION_CLASS The session class . This may be used instead of class= on the module parameter line, and is usually preferred .
$XDG_SESSION_DESKTOP The desktop identifier . This may be used instead of desktop= on the module parameter line, and is usually preferred .
$XDG_SEAT The seat name the session shall be registered for, if any .
$XDG_VTNR 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 pam_systemd.so ,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 (Aqs 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 .
systemd.memory_max Sets unit MemoryMax= .
systemd.tasks_max Sets unit TasksMax= .
systemd.cpu_weight Sets unit CPUWeight= .
systemd.io_weight Sets unit IOWeight= .
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 -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 .RE
" 1." 4 Desktop Entry Specification http://standards.freedesktop.org/desktop-entry-spec/latest/
" 2." 4 XDG Base Directory Specification http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html