capsule@.service - System unit for the capsule service manager

capsule@NAME.service

Service managers for capsules run in capsule@NAME.service 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.

In many ways capsule@.service is similar to the per-user user@.service service manager, but there are a few important distinctions:

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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.

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User service managers register themselves with pam(8), capsule service managers do not.

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User service managers typically read their configuration from a $HOME directory below /home/, capsule service managers from a $HOME directory below /var/lib/capsules/.

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User service managers are collectively contained in the user.slice unit, capsule service managers in capsule.slice. Also see systemd.special(7).

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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 capsules 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/NAME/, if missing. A runtime directory is created as /run/capsules/NAME/. To remove these resources use systemctl clean capsule@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 "c-" be suitable as a user name matching strict POSIX rules, see User/Group Name Syntax[1] for details.

Added in version 256.

Example 1. Create a new capsule, invoke two programs in it (one interactively), terminate it, and clean everything up

.RS 4

# 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

.RE

systemd(1), user@.service(5), systemd.service(5), systemd.slice(5), systemd.exec(5), systemd.special(7), systemctl(1), systemd-run(1), busctl(1), pam(8)