PAM_SYSTEMD(8) pam_systemd PAM_SYSTEMD(8)
NAME
pam_systemd - Register user sessions in the systemd login manager
SYNOPSIS
pam_systemd.so
DESCRIPTION
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 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 logging in.
2. The $XDG_SESSION_ID environment variable is initialized. If
auditing is available and pam_loginuid.so was run before this
module (which is highly recommended), the variable is initialized
from the auditing session id (/proc/self/sessionid). Otherwise, an
independent session counter is used.
3. A new systemd scope unit is created for the session. If this is the
first concurrent session of the user, an implicit per-user slice
unit below user.slice is automatically created and the scope placed
into it. An instance of the system service user@.service, which
runs the systemd user manager instance, is started.
4. The "$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.
OPTIONS
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 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.
debug[=]
Takes an optional boolean argument. If yes or without the argument,
the module will log debugging information as it operates.
MODULE TYPES PROVIDED
Only session is provided.
ENVIRONMENT
The following environment variables are initialized by the module and
available to the processes of the user's 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'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.
$XDG_SESSION_TYPE
The session type. This may be used instead of type= 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).
SESSION LIMITS
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.
systemd.memory_max=
Sets unit MemoryMax=.
systemd.tasks_max=
Sets unit TasksMax=.
systemd.cpu_weight=
Sets unit CPUWeight=.
systemd.io_weight=
Sets unit IOWeight=.
systemd.runtime_max_sec=
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);
EXAMPLE
Here's an example PAM configuration fragment that allows users sessions
to be managed by systemd-logind.service:
#%PAM-1.0
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 try_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
SEE ALSO
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), systemd.service(5)
NOTES
1. JSON User Record
https://systemd.io/USER_RECORD
2. Desktop Entry Specification
http://standards.freedesktop.org/desktop-entry-spec/latest/
3. XDG Base Directory Specification
http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
systemd 245 PAM_SYSTEMD(8)