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USER@.SERVICE(5) user@.service USER@.SERVICE(5)
NAME
user@.service, user-runtime-dir@.service, systemd-user-runtime-dir - System units to start
the user manager
SYNOPSIS
user AT UID.service
user-runtime-dir AT UID.service
/lib/systemd/systemd-user-runtime-dir
user-UID.slice
DESCRIPTION
The systemd(1) system manager (PID 1) starts user manager instances as user AT UID.service,
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.
user AT UID.service is accompanied by the system unit user-runtime-dir AT UID.service, which
creates the user's runtime directory /run/user/UID, and then removes it when this unit is
stopped. user-runtime-dir AT UID.service executes the systemd-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 AT UID.service and the scope units are collected under the
user-UID.slice.
Individual user-UID.slice slices are collected under user.slice, see systemd.special(7).
CONTROLLING RESOURCES FOR LOGGED-IN USERS
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-UID.slice. Resource limits for
that user can be configured through drop-ins for that unit, e.g.
/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-UID.slice units,
see systemd.unit(5) for a discussion of the drop-in mechanism.
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 AT UID.service and the slice
units discussed above, see systemd.resource-control(5) for an overview.
EXAMPLES
Example 1. Hierarchy of control groups with two logged in users
$ systemd-cgls
Control group /:
-.slice
user.slice
| user-1000.slice
| | user AT 1000.service
| | | pulseaudio.service
| | | | 2386 /usr/bin/pulseaudio --daemonize=no
| | | gnome-terminal-server.service
| | | init.scope
| | | 4127 /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 AT 1001.service
| init.scope
| | 6680 /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 AT 1000.service). User with UID 1001 is
logged in using ssh (session-20.scope) and also has a user manager instance running
(user AT 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
# /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-UID.slice 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.
SEE ALSO
systemd(1), systemd.service(5), systemd.slice(5), systemd.resource-control(5),
systemd.exec(5), systemd.special(7), pam(8)
systemd 249 USER@.SERVICE(5)
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