pam_systemd — Register user sessions in the systemd login manager
pam_systemd.so
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:
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.
The $XDG_SESSION_ID environment variable is initialized. If auditing is
available and pam_loginuid.so was run before this module (which is highly recommended), the
variable is initialized from the auditing session id (/proc/self/sessionid). Otherwise, an
independent session counter is used.
A new systemd scope unit is created for the session. If this is the first concurrent session of
the user, an implicit per-user slice unit below user.slice is automatically created and the
scope placed into it. An instance of the system service user@.service, which runs the
systemd user manager instance, is started.
On logout, this module ensures the following:
If enabled in
logind.conf(5) (KillUserProcesses=), all processes of the session are
terminated. If the last concurrent session of a user ends, the user's systemd instance will be terminated too,
and so will the user's slice unit.
If the last concurrent session of a user ends,
the user runtime directory /run/user/$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 environmental variable 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 environmental variable takes
precedence. One of
"unspecified",
"tty",
"x11",
"wayland" or
"mir". See
sd_session_get_type(3)
for details about the session type.
debug[=]¶Takes an optional boolean argument. If yes or without the argument, the module will log debugging information as it operates.
The following environment variables are set for the processes of the user's session:
$XDG_SESSION_ID¶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.
$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'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. $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:
$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¶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. (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.
$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 determine the
values for $XDG_SEAT and $XDG_VTNR
based on the $DISPLAY variable.
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'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.
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