pam_systemd - Register user sessions in the systemd login
pam_systemd registers user sessions with the systemd login
manager systemd-logind.service(8), and hence the systemd control
The module also applies various resource management and runtime
parameters to the new session, as configured in the JSON User
Records of the user, when one is defined.
On login, this module — in conjunction with
systemd-logind.service — ensures the following:
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
2.The $XDG_SESSION_ID environment variable is
initialized. If auditing is available and pam_loginuid.so was run
before this module (which is highly recommended), the variable is initialized
from the auditing session id (/proc/self/sessionid). Otherwise, an independent
session counter is used.
3.A new systemd scope unit is created for the session.
If this is the first concurrent session of the user, an implicit per-user
slice unit below user.slice is automatically created and the scope placed into
it. An instance of the system service user@.service, which runs the systemd
user manager instance, is started.
4.The "$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)
), 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,
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
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
environment variable (see below) takes precedence. One
of "unspecified", "tty", "x11",
"wayland" or "mir". See sd_session_get_type(3)
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
. (However, note that the option
only takes a single item, and not a colon-separated list like
.) See sd_session_get_desktop(3)
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
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.
$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
The VT number the session shall be registered for, if
any. (Only applies to seats with a VT available, such as
If not set, pam_systemd will initialize $XDG_SEAT
and $XDG_VTNR based on the $DISPLAY variable (if the latter is
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
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 systemd-logind.service:
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
logind.conf(5), loginctl(1), pam_systemd_home(8),
pam.conf(5), pam.d(5), pam(8), pam_loginuid(8),
- JSON User Records
- Desktop Entry Specification
- XDG Base Directory Specification