[Trilug-ontopic] sysadmin questions

[Richard O. Hammer]

Hi,

I'm trying to set up some linux servers and have questions which are probably 
basic to most of you.  Please let me know if this is not the appropriate place 
to ask such questions.

What is the relationship between the user's group as designated in these two 
places:
  1. in /etc/passwd in the fourth field in the line for a given user, and
  2. in /etc/group, listed in the last field in the line for a given group?

I've created a test user (useradd -g testgroup testuser).  Now I see the group 
number for testgroup listed in /etc/passwd on the testuser line.  But I don't 
see "testuser" in /etc/group on the testgroup line.

Can a user belong to several groups?  What command does the trick?

Can a group belong to a group?  What command does this trick?

Perhaps this is amusing: On running "man group" I get a man page, evidently 
dated December 1992, which says (among other things)
BUGS  As the 4.2BSD initgroups(3) man page says: No-one seems to keep /etc/group 
up-to-date.

I'm using CentOS5 on a server rented from RIMUhosting.com.

Thank you,
Rich Hammer
Hillsborough