Manual: pam_systemd
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 Records[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. 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-light │ Similar to user, but sessions of this │
│ │ class will not pull in the │
│ │ user@.service(5) of the user, and thus │
│ │ possibly have no service manager of the │
│ │ user running. (Added in v258.) │
├──────────────────┼───────────────────────────────────────────┤
│ user-early-light │ Similar to user-early, but sessions of │
│ │ this class will not pull in the │
│ │ user@.service(5) of the user, and thus │
│ │ possibly have no service manager of the │
│ │ user running. (Added in v258.) │
├──────────────────┼───────────────────────────────────────────┤
│ 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 service manager 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.) │
├──────────────────┼───────────────────────────────────────────┤
│ none │ Skips registering this session with │
│ │ logind. No session scope will be created, │
│ │ and the user service manager will not be │
│ │ started. (Added in v258.) │
└──────────────────┴───────────────────────────────────────────┘
If no session class is specified via either the PAM module option or via the $XDG_SESSION_CLASS environment
variable, the class is automatically chosen, depending on various session parameters, such as the session type
(if known), whether the session has a TTY or X11 display, and the user disposition. Note that various tools allow
setting the session class for newly allocated PAM sessions explicitly by means of the $XDG_SESSION_CLASS
environment variable. For example, classic UNIX cronjobs support environment variable assignments (see
crontab(5)), which may be used to choose between the background and background-light session class individually
per cronjob, or run0 --setenv=XDG_SESSION_CLASS=user-light may be used to choose between user and user-light for
invoked privileged sessions.
Added in version 197.
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.
Added in version 209.
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.
Added in version 240.
area=
Takes a filename as parameter. If specified and the user logs into their account the $HOME environment variable
will be set to ~/Areas/ suffixed by the specified string, but only if that directory exists. Moreover, the
$XDG_AREA variable will be set to the (unprefixed) parameter.
This functionality may be used to maintain multiple separate secondary home directories within the primary home
directory of the user. Typically, the area to log into is specified while logging in, if the account permits that
(accounts provided by pam_systemd_home(8) do), but this parameter may be used to define a default if that's not
provided.
Note that this only adjusts $HOME during login, it does not affect the otherwise reported home directory of the
user. Specifically this means that sshd(8) will continue to look for SSH keys of the user only in the primary
home directory of the user, not in any of their areas.
Note that the default area to log into can also be configured as part of the user account. The area specified via
area= overrides the default area configured there. Also note that if the area is specified explicitly by the user
at login time, it overrides both. Also note that setting this parameter to an empty string has the effect of
undoing the effect of any default area configured as part of the user record, i.e. ensuring the user logs into
the primary home directory of their account.
For details on the area concept see pam_systemd_home(8).
Added in version 258.
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
user@.service. Otherwise, defaults to the empty set.
Added in version 254.
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.
$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.
Added in version 245.
$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.
Added in version 257.
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.
Added in version 209.
$XDG_SESSION_CLASS
The session class. This may be used instead of class= on the module parameter line, and is usually preferred.
Added in version 209.
$XDG_SESSION_DESKTOP
The desktop identifier. This may be used instead of desktop= on the module parameter line, and is usually
preferred.
Added in version 209.
$XDG_SEAT
The seat name the session shall be registered for, if any.
Added in version 209.
$XDG_VTNR
The VT number the session shall be registered for, if any. (Only applies to seats with a VT available, such as
"seat0")
Added in version 209.
$XDG_AREA
If an area (secondary home directories of the user, within the primary home directory) to log into has been
selected this variable is set to the area name (without any path prefix). It is otherwise unset. For details
about areas, see above.
Added in version 258.
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=.
Added in version 239.
systemd.tasks_max=
Sets unit TasksMax=.
Added in version 239.
systemd.cpu_weight=
Sets unit CPUWeight=.
Added in version 239.
systemd.io_weight=
Sets unit IOWeight=.
Added in version 239.
systemd.runtime_max_sec=
Sets unit RuntimeMaxSec=.
Added in version 244.
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 [success=done authtok_err=bad perm_denied=bad maxtries=bad default=ignore] pam_systemd_home.so
auth sufficient pam_unix.so
auth required pam_deny.so
account required pam_nologin.so
-account [success=done authtok_expired=bad new_authtok_reqd=bad maxtries=bad acct_expired=bad default=ignore] pam_systemd_home.so
account required pam_unix.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
SEE ALSO
systemd(1), systemd-user-sessions.service(8), user@.service(5), 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 Records
https://systemd.io/USER_RECORD
2. Desktop Entry Specification
https://standards.freedesktop.org/desktop-entry-spec/latest/
3. XDG Base Directory Specification
https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
systemd 259.5 PAM_SYSTEMD(8)