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.
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:
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 $XDG_SESSION_ID environment variable is initialized. If auditing is
available and pam_loginuid.so was run before this module (which is highly recommended), the
variable is initialized from the auditing session id (/proc/self/sessionid). Otherwise, an
independent session counter is used.
A new systemd scope unit is created for the session. If this is the first concurrent session of
the user, an implicit per-user slice unit below user.slice is automatically created and the
scope placed into it. An instance of the system service user@.service, which runs the
systemd user manager instance, is started.
The "$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:
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 environment variable (see below) takes precedence. See
sd_session_get_class(3)
for a way to query the class of a session. The following session classes are defined:
Table 1. Session Classes
| Name | Explanation |
|---|---|
user | A regular interactive user session. This is the default class for sessions for which a TTY or X display is known at session registration time. |
user-early | Similar to "user" but sessions of this class are not ordered after systemd-user-sessions.service(8), i.e. may be started before regular sessions are allowed to be established. This session class is the default for sessions of the root user that would otherwise qualify for the user class, see above. (Added in v256.) |
user-incomplete | Similar to "user" but for sessions which are not fully set up yet, i.e. have no home directory mounted or similar. This is used by systemd-homed.service(8) to allow users to log in via ssh(1) before their home directory is mounted, delaying the mount until the user provided the unlock password. Sessions of this class are upgraded to the regular user class once the home directory is activated. |
greeter | Similar to "user" but for sessions that are spawned by a display manager ephemerally and which prompt the user for login credentials. |
lock-screen | Similar to "user" but for sessions that are spawned by a display manager ephemerally and which show a lock screen that can be used to unlock locked user accounts or sessions. |
background | Used for background sessions, such as those invoked by cron(8) and similar tools. This is the default class for sessions for which no TTY or X display is known at session registration time. |
background-light | Similar to background, but sessions of this class will not pull in the user@.service(5) of the user, and thus possibly have no services of the user running. (Added in v256.) |
manager | The user@.service(5) service of the user is registered under this session class. (Added in v256.) |
manager-early | Similar to manager, but for the root user. Compare with the user vs. user-early situation. (Added in v256.) |
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", "mir", or
"web". 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. (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.
default-capability-bounding-set=, default-capability-ambient-set=¶Takes a comma-separated list of process capabilities
(e.g. CAP_WAKE_ALARM, CAP_BLOCK_SUSPEND, …) to set for the
invoked session's processes, if the user record does not encode appropriate sets of capabilities
directly. See capabilities(7)
for details on the capabilities concept. If not specified, the default bounding set is left as is
(i.e. usually contains the full set of capabilities). The default ambient set is set to
CAP_WAKE_ALARM for regular users if the PAM session is associated with a local
seat or if it is invoked for the "systemd-user" service. Otherwise defaults to the
empty set.
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 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.
$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.
$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.
$SHELL_PROMPT_PREFIX, $SHELL_PROMPT_SUFFIX, $SHELL_WELCOME¶These environment variables are initialized from the service credentials
"shell.prompt.prefix", "shell.prompt.suffix" and
"shell.welcome" if set. They are passed to the invoked session processes, where they
are imported into any shell prompt (specifically $SHELL_PROMPT_PREFIX is added as
prefix to $PS1, and $SHELL_PROMPT_SUFFIX as suffix) or printed
on screen when a shell first initializes.
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).
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_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:
#%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
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