I always write the following statement. I am learning Linux from Christopher Negus's Linux Bible. When I am providing id command then along with my uid, gid and groups some other information are also coming like
From a source on internet I have found that
How numbers are chosen and what do they mean beside each such element within bracket. Like 24(cdrom Use CD-ROM drives) what is the actual meaning?

probably this helps: https://linoxide.com/linux-id-command/

Hi again 'learner'! Here's a couple of general Thots (thoughts) I have to offer, on the 'soft skill' of beginner learning:

Formulate/compose a web-search that includes the essential keywords for your topic.
Try it (google, duckduckgo etc), to discover & refine more/other (or less) keywords.
Then I'd include it in my LQ post, like:

historically how group gid numbers chosen meaning unix|linux

(you might use 'advanced' search features, like quoting to require "chosen", and my use of | as or). Maybe other LQ'ers will help you refine it (if needed). And others can then (roughly) see the search results that you see, for discussion.


My other thot is that it's not essential to (initially) fully understand every (minor) detail (there's zillions). Certainly read the man page. (A last&expert resource is the source code, unlike M$Windows, so it's possible to get to the bottom on anything, with enough digging, although you'd probably want to move on to the next of thousands of topics!)


Enjoy learning (I do!).



p.s. as an answer here, you could search (for each group):

adm linux group
sudo adm unix group permissions

to research what each does/enables. It took me a lot of trying, but I finally found one webpage that explains a lot of them:

https://wiki.debian.org/SystemGroups

And this (advanced info) by searching your entire quote block content! &this

https://www.geeksforgeeks.org/id-com...with-examples/

https://geek-university.com/linux/ui...up-identifier/

I was thinking it is that book which contains answers to these questions. Myself I never read that book - difficult to tell for me. What kind of Linux Bible is it? If as it seems from OP questions does not fundamental information about Linux.

Edit: From my side I can promise yet another thread of OP mentioning that book I will report as advertisement.

By convention (which actually in some parts predates Linux). From LSB 4.1:
Also see https://en.wikipedia.org/wiki/User_i...er#Conventions

For details, see this discussion at Red Hat Customer Portal and the documents linked from there. Some of the links may be dead by now, but the information is easy to find, nevertheless.

Debian Wiki has a page describing the purpose of many system groups. And the README from package base-passwd provides additional information.

The only thing I'd add is that most (if not all) Linux distros now start user accts at id = 1000 .
For RHEL this changed for v7; v6 started at 500 see /etc/login.defs.