Is there any way i can list all the user groups on the system, not using the GUI interface...i need to get all the user group names as part of a program I'm working on...

I'm in the system administrator mode...

I need to read all the user groups into a user interface that I'm creating...

Thanks

Debdas

Sounds very... suspicious. However, it's really not that big of a deal I guess if you've already cracked into the system with root access...

Anyway, the users are listed in /etc/passwd
You can view this by typing:
cat /etc/passwd
OR
less /etc/passwd

Cool

If you want to view the groups (if I have read your question wrong the first time), the file is:
/etc/groups
And to find which ones are user(s) groups normally these are 500+. However, you could also compare your UID's with corresponding GID's.

Cool

<edit>
And you shouldn't post your question in more than 1 forum. I understand you "reworded" it, however it's virtually the same question.
</edit>

I know that /etc/passwd contains the group names and that 500+ group ids are user group ids. But they can be modified to any number... So how can I be sure that they are actually user group ids only.

I changed the group id of a user group to a number less than 500(81 precisely) and found that the Users and Groups interface under System Tools did not display the user group. Why????

I need only the user group names to store some data corresponding to each group in a file that is similar to /etc/passwd. I am trying to develop an interface that will recognise all the user groups existing on the system and read certain data associated with each user group.

Why is this so suspicious ????

well it didn't show the users as you changed the GID to less 500, that *IS* the reason. it ranges of numbers are a convention that works pretty well as long as it is respected. not all rules are there to be broken... sure you can change the gid to whatever you want, but you shouldn't.. just like you should ever run "cat /dev/random > /dev/hda1"...