The systemd(1) system manager (PID 1) starts user manager instances
as user@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@UID.service is accompanied by the system unit
user-runtime-dir@UID.service, which creates the user's runtime
directory /run/user/UID, and then removes it when this unit is
stopped. user-runtime-dir@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@UID.service and the scope units are
collected under the user-UID.slice.
Individual user-UID.slice slices are collected under user.slice, see
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.
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@UID.service and the slice units discussed above, see
systemd.resource-control(5) for an overview.
Example 1. Hierarchy of control groups with two logged in users
Control group /:
│ │ ├─firstname.lastname@example.org
│ │ │ ├─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
│ │ ├─6675 sshd: guest [priv]
│ │ ├─6708 sshd: guest@pts/6
│ │ └─6717 -bash
│ │ ├─6680 /usr/lib/systemd/systemd --user
│ │ └─6688 (sd-pam)
│ └─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 (email@example.com). User with UID 1001 is logged in using
ssh (session-20.scope) and also has a user manager instance running
(firstname.lastname@example.org). 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,
Example 2. Default user resource limits
$ systemctl cat user-1000.slice
Description=User Slice of UID %j
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.
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-07-14. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-07-14.) If you discover any rendering problems in
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of the original manual page), send a mail to email@example.com
systemd 246 USER@.SERVICE(5)