[RFC] screen: don't enable multiuser mode by default.

[ericonr]

This requires that the screen binary be suid.

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR

[tornaria]

This actually prevents screen from running at all:

$ screen
Cannot make directory '/run/screens': Permission denied

Ideas:

• Maybe some init script should mkdir -m 1777 /run/screens at startup?
• Maybe removing --with-socket-dir=/run/screens would use an alternative default which works for all users?

[ericonr]

Damnit, I only tested when the directory already existed :/

[ericonr]

Maybe removing --with-socket-dir=/run/screens would use an alternative default which works for all users?

Would be nice but breaks existing sessions unless the person sets SCREENDIR. I think that's worse...

Maybe some init script should mkdir -m 1777 /run/screens at startup?

Good enough, IMO.

[tornaria]

I also like the mkdir choice better, because it allows one to easily reenable multiuser screen by just making the binary setuid.

Note that since /run is cleaned at reboots (or a tmpfs) the directory has to be created at every boot, not at install time.

[ericonr]

I am opening a PR in a bit. Initially I went with removing socket-dir, but realized the potential for breakage.

[ericonr]

@tornaria #32159