user@.service, user-runtime-dir@.service, systemd-user-runtime-dir — System units to start the user manager
user@UID.service
user-runtime-dir@UID.service
/usr/lib/systemd/systemd-user-runtime-dir
user-UID.slice
The systemd(1)
system manager (PID 1) starts user manager instances as
user@, with the user's numerical UID used as
the instance identifier. These instances use the same executable as the system manager, but running in a
mode where it starts a different set of units. Each systemd --user instance manages a
hierarchy of units specific to that user. See
systemd(1) for a
discussion of units and
systemd.special(7) for a
list of units that form the basis of the unit hierarchies of system and user units.UID.service
user@ is accompanied by the
system unit UID.serviceuser-runtime-dir@, which
creates the user's runtime directory
UID.service/run/user/, and then removes it when this
unit is stopped. UIDuser-runtime-dir@
executes the UID.servicesystemd-user-runtime-dir binary to do the actual work.
User processes may be started by the user@.service instance, in which
case they will be part of that unit in the system hierarchy. They may also be started elsewhere,
for example by
sshd(8) or a
display manager like gdm, in which case they form a .scope unit (see
systemd.scope(5)).
Both user@ and the scope units are
collected under the UID.serviceuser-.UID.slice
Individual user- slices are
collected under UID.sliceuser.slice, see
systemd.special(7).
Options that control resources available to logged-in users can be configured at a few
different levels. As described in the previous section, user.slice contains
processes of all users, so any resource limits on that slice apply to all users together. The
usual way to configure them would be through drop-ins, e.g. /etc/systemd/system/user.slice.d/resources.conf.
The processes of a single user are collected under
user-. Resource limits for that user
can be configured through drop-ins for that unit, e.g. UID.slice/etc/systemd/system/user-1000.slice.d/resources.conf. If the limits
should apply to all users instead, they may be configured through drop-ins for the truncated
unit name, user-.slice. For example, configuration in /etc/systemd/system/user-.slice.d/resources.conf is included in all
user- units, see
systemd.unit(5)
for a discussion of the drop-in mechanism.UID.slice
When a user logs in and a .scope unit is created for the session (see previous section), the creation of the scope may be managed through pam_systemd(8). This PAM module communicates with systemd-logind(8) to create the session scope and provide access to hardware resources. Resource limits for the scope may be configured through the PAM module configuration, see pam_systemd(8). Configuring them through the normal unit configuration is also possible, but since the name of the slice unit is generally unpredictable, this is less useful.
In general any resources that apply to units may be set for
user@ and the slice
units discussed above, see
systemd.resource-control(5)
for an overview.UID.service
Example 1. Hierarchy of control groups with two logged in users
$ systemd-cgls Control group /: -.slice ├─user.slice │ ├─user-1000.slice │ │ ├─user@1000.service │ │ │ ├─pulseaudio.service │ │ │ │ └─2386 /usr/bin/pulseaudio --daemonize=no │ │ │ └─gnome-terminal-server.service │ │ │ └─init.scope │ │ │ ├─ 4127 /usr/libexec/gnome-terminal-server │ │ │ └─ 4198 zsh │ │ … │ │ └─session-4.scope │ │ ├─ 1264 gdm-session-worker [pam/gdm-password] │ │ ├─ 2339 /usr/bin/gnome-shell │ │ … │ │ ├─session-19.scope │ │ ├─6497 sshd: zbyszek [priv] │ │ ├─6502 sshd: zbyszek@pts/6 │ │ ├─6509 -zsh │ │ └─6602 systemd-cgls --no-pager │ … │ └─user-1001.slice │ ├─session-20.scope │ │ ├─6675 sshd: guest [priv] │ │ ├─6708 sshd: guest@pts/6 │ │ └─6717 -bash │ └─user@1001.service │ ├─init.scope │ │ ├─6680 /usr/lib/systemd/systemd --user │ │ └─6688 (sd-pam) │ └─sleep.service │ └─6706 /usr/bin/sleep 30 …
User with UID 1000 is logged in using gdm (session-4.scope) and
ssh(1)
(session-19.scope), and also has a user manager instance
running (user@1000.service). User with UID 1001 is logged
in using ssh (session-20.scope) and
also has a user manager instance running (user@1001.service). Those are all (leaf) system units, and form
part of the slice hierarchy, with user-1000.slice and
user-1001.slice below user.slice. User units are visible below the
user@.service instances (pulseaudio.service, gnome-terminal-server.service, init.scope, sleep.service).
Example 2. Default user resource limits
$ systemctl cat user-1000.slice # /usr/lib/systemd/system/user-.slice.d/10-defaults.conf # … [Unit] Description=User Slice of UID %j After=systemd-user-sessions.service [Slice] TasksMax=33%
The user- units by default don't
have a unit file. The resource limits are set through a drop-in, which can be easily replaced
or extended following standard drop-in mechanisms discussed in the first section.UID.slice