groups - which does what?

uxer

apropos hasn't helped me.
The internet is scarce on it.

https://wiki.archlinux.org/title/Users_and_groups
has it, but:

it doesn't contain e.g. the staff and operator group, so I guess it may have omitted more
it is not (Open)BSD, and furthermore it has additional systemd-related noise

1. Where can I find a description of what each group does?

2. `video`

This:
https://www.unitedbsd.com/d/673-poor-mans-browser-sandboxing
https://www.dragonflybsd.org/docs/handbook/RunSecureBrowser/
mentions video group for GPU acceleration. Without sandboxing, on a regular install, my user is not in video group, yet chrome://gpu/ shows 3 Hardware accelerated entries. Why?

3. `games`

I need /usr/games/fortune, had to add /usr/games to my PATH for fortune to work without full path.
Group games affects /var/games and not /usr/games.
So how has it happened that there is games install set, and group games which are not affiliated and you still have to add /usr/games to PATH manually? Or have I missed something?

4. What is the difference between `group` vs `class`?

https://docs.freebsd.org/en/books/handbook/basics/

Login classes are an extension to the group mechanism that provide additional flexibility when tailoring the system to different users.

Any more elaborate - yet concise - description?

5. `id -Gn [user]`

Why groups or id -Gn print <username> wheel staff when whoami is <username> whereas
groups <username> or id -Gn <username> print <username> wheel without staff?

rvp

uxer

Some of the groups are either a) historical, or b) for use by packages which may be added later on: for example group staff doesn't own any files in a "usual" OpenBSD install (try find / -group staff), but, the whole ports tree belongs to `staff--if you unpack that set.
Group video is present only of FreeBSD/DragonflyBSD. On OpenBSD the /dev/dri/* files are wheel-writable, and you probably are a member of wheel.
Group games is for games which keep a high-scores list. It's also used by dm. All these programs will be setgid to games. As to why /usr/games is not in the default PATH? No idea. But, you can add that either in the profile skeleton files or using the login.conf functionality.
class is a user-level feature used to setup different system limits or environments at login-time. The kernel only understands groups.
Good question...Dunno.