Where to find purpose of each system default Groups and Users in Linux

Question

when I cat /etc/group and cat /etc/passwd I get a list in which I find many I don't know. I know only group sudo group. But there is are many which I don't knows such as sys, adm .... I like to learn about them. But I did not find a good article online. Is there any specific documentation or man page to learn about them.

Answer 1

The answer depends on what system you’re using; there are a number of Q&As on the topic, on this site, such as:

• How to know which users / groups can safely be deleted?
• What Users should be expected in /etc/group adm: group
• Which users are necessary on Unix/Linux?
• What is the Debian counterpart of the admin group, and what group on Debian makes files accessible to only the owner and the administrators?

and on Retrocomputing.SE: What was the purpose of those special user accounts in Unix?

For Debian specifically, the default groups and users are documented in users-and-groups.sgml which is shipped as /usr/share/doc/base-passwd/users-and-groups.txt.gz on installed systems.