pam_systemd — Register user sessions in the systemd control group hierarchy
pam_systemd.so
pam_systemd registers user sessions in the systemd control group hierarchy.
On login, this module ensures the following:
If it does not exist yet, the
user runtime directory
/run/user/$USER
is
created and its ownership changed to the user
that is logging in.
If
create-session=1
is set, the
$XDG_SESSION_ID
environment
variable is initialized. If auditing is
available and
pam_loginuid.so run before
this module (which is highly recommended), the
variable is initialized from the auditing
session id
(/proc/self/sessionid
). Otherwise
an independent session counter is
used.
If
create-session=1
is set, a new
control group
/user/$USER/$XDG_SESSION_ID
is created and the login process moved into
it.
If
create-session=0
is set, a new
control group
/user/$USER/user
is created and the login process moved into
it.
On logout, this module ensures the following:
If
$XDG_SESSION_ID
is set and
kill-session=1
specified, all
remaining processes in the
/user/$USER/$XDG_SESSION_ID
control group are killed and the control group
is removed.
If
$XDG_SESSION_ID
is set and
kill-session=0
specified, all
remaining processes in the
/user/$USER/$XDG_SESSION_ID
control group are migrated to
/user/$USER/user
and
the original control group is
removed.
If
kill-user=1
is specified, and
no other user session control group remains,
except
/user/$USER/user
,
all remaining processes in the
/user/$USER
hierarchy
are killed and the control group is removed.
If
kill-user=0
is specified, and
no process remains in the
/user/$USER
hierarchy the
control group is removed.
If the
/user/$USER
control group
was removed the
$XDG_RUNTIME_DIR
directory
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:
create-session=
Takes a boolean
argument. If true, a new session is
created: the
$XDG_SESSION_ID
environment variable is set and the
login process moved to the
/user/$USER/$XDG_SESSION_ID
control group. It is recommended that
all services which are directly created
on the user's behalf set this
option. Only for services that shall
automatically be terminated when the
user logs out completely, otherwise
create-session=0
should be set.
kill-session=
Takes a boolean argument. If true, all processes created by the user during his session and from his session will be terminated when he logs out from his session.
kill-user=
Takes a boolean
argument. If true, all processes
created by the user during his session
and from his session will be
terminated after he logged out
completely. This is a weaker version
of kill-session=1
and is
more friendly for users logged in more
than once, as their processes are
terminated only on their complete
logout.
kill-only-users=
Takes a comma
separated list of user names or
numeric user ids as argument. If this
option is used the effect of the
kill-session=
and
kill-user=
options
will apply only to the listed
users. If this option is not used the
option applies to all local
users. Note that
kill-exclude-users=
takes precedence over this list and is
hence subtracted from the list
specified here.
kill-exclude-users=
Takes a comma
separated list of user names or
numeric user ids as argument. Users
listed in this argument will not be
subject to the effect of
kill-session=
or
kill-user=
. Note
that that this option takes precedence
over
kill-only-users=
, and
hence whatever is listed for
kill-exclude-users=
is guaranteed to never be killed by
this PAM module, independent of any
other configuration
setting.
controllers=
Takes a comma separated list of cgroup controllers in which hierarchies a user/session cgroup will be created by default for each user logging in, in addition to the cgroup in the named 'name=systemd' hierarchy. If ommited, defaults to an empty list. This may be used to move user sessions into their own groups in the 'cpu' hierarchy which ensures that every logged in user gets an equal amount of CPU time regardless how many processes he has started.
reset-controllers=
Takes a comma separated list of cgroup controllers in which hierarchies the logged in processes will be reset to the root cgroup. If ommited, defaults to 'cpu', meaning that a 'cpu' cgroup grouping inherited from the login manager will be reset for the processes of the logged in user.
Note that setting kill-user=1
or even kill-session=1
will break
tools like
screen(1).
If the options are omitted they default to
create-session=1
,
kill-session=0
,
kill-user=0
,
reset-controllers=cpu
,
kill-only-users=
,
kill-exclude-users=root
.
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 file names. 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 his 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
behaviour 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.