capsule@.service — System unit for the capsule service manager
capsule@NAME.service
Service managers for capsules run in
capsule@ system units, with the capsule name as the
instance identifier. Capsules are way to run additional instances of the service manager, under dynamic
user IDs, i.e. UIDs that are allocated when the capsule service manager is started, and released when it
is stopped.NAME.service
In many ways capsule@.service is similar to the per-user
user@.service service manager, but there are a few important distinctions:
The capsule service manager utilizes DynamicUser= (see
systemd.exec(5)) to
allocate a new UID dynamically on invocation. The user name is automatically generated from the capsule
name, by prefixing "c-". The UID is released when the service is terminated. The user
service manager on the other hand operates under a statically allocated user ID that must be
pre-existing, before the user service manager is invoked.
User service managers register themselves with pam(8), capsule service managers do not.
User service managers typically read their configuration from a
$HOME directory below /home/, capsule service managers from a
$HOME directory below /var/lib/capsules/.
User service managers are collectively contained in the user.slice
unit, capsule service managers in capsule.slice. Also see
systemd.special(7).
User service managers start the user unit default.target
initially. Capsule service managers invoke the user unit capsule@.target
instead.
The capsule service manager and the capsule's bus broker can be reached via the
--capsule= switch to
systemctl(1),
systemd-run(1) and
busctl(1).
New capsules can be started via a simple systemctl start
capsule@NAME.service command, and stopped via systemctl
stop capsule@NAME.service. Starting a capsule will implicitly create
a home directory /var/lib/capsules/, if missing. A
runtime directory is created as NAME//run/capsules/. To
remove these resources use systemctl clean capsule@NAME/NAME.service,
for example with the --what=all switch.
The capsule@.service unit invokes a systemd --user
service manager process. This means unit files are looked for according to the sames rules as for regular user
service managers, for example in
/var/lib/capsules/.NAME/.config/systemd/user/
Capsule names may be chosen freely by the user, however, they must be suitable as UNIX filenames
(i.e. 255 characters max, and contain no "/"), and when prefixed with
"p-" be suitable as a user name matching strict POSIX rules, see User/Group Name Syntax for details.
Example 1. Create a new capsule, invoke two programs in it (one interactively), terminate it, and clean everything up
# systemctl start capsule@tatze.service # systemd-run --capsule=tatze --unit=sleeptest.service sleep 999 # systemctl --capsule=tatze status sleeptest.service # systemd-run -t --capsule=tatze bash # systemctl --capsule=tatze stop sleeptest.service # systemctl stop capsule@tatze.service # systemctl clean --all capsule@tatze.service