This adds a new --lightweight=yes/no switch which allows controlling
whether the invoked service will have the service manager around or not.
Moreover, this changes that if the target user is root it will now
support to the lightweight mode, i.e. run0 towards root will no longer
pull in the service manager (a real tty login via getty still will
though!).
My thinking here is that quickly raising privileges via run0 probably
shouldn't be considered a proper login but just something short lived,
temporary for a single command or similar.
This makes use of the infra introduced in 229d4a9806 to indicate visually on each prompt that we are in superuser mode temporarily.
pick ad5de3222f userdbctl: add some basic client-side filtering
For run0 (as opposed to systemd-run in general), connecting to
the system bus (of localhost or container) as a different user
than root and then trying to elevate privilege from that
makes little sense:
https://github.com/systemd/systemd/issues/32997#issuecomment-2127992973
The @ syntax is mostly useful when connecting to the user bus,
which is not a use case for run0. Hence, let's remove the example.
The syntax will be properly refused in #32999.
Naming is always a matter of preference, and the old name would certainly work,
but I think the new one has the following advantages:
- A verb is better than a noun.
- The name more similar to "the competition", i.e. 'sudo', 'pkexec', 'runas',
'doas', which generally include an action verb.
- The connection between 'systemd-run' and 'run0' is more obvious.
There has been no release yet with the old name, so we can rename without
caring for backwards compatibility.
