UNIX for Advanced & Expert Users

I m usi ng RHEL 4 and /etc/group file contains line 7000 characters.
so it is possible to have a 1000 user in single group

I'm not sure what you are asking - /etc/group is supposed to be limited to LINE_MAX bytes per line. So LINE_MAX bytes can be used to describe users in the group. Check your man page.

Code:

getconf LINE_MAX

shows your system's value for this.

The record layout is:

Code:

group_name:passwd:GID:user_list

where user_list is a comma delimited list of user names in the group.

Where does 1000 come in? LINE_MAX and username length (plus a comma) are the limiting factors. 7000 bytes in a line and 5 character usernames (if allowed) will give 1000+.

There is no limit on the number of users in a primary group. The limit of LINE_MAX applies to each secondary group. It is not necessary or advisible to list any users primary group in /etc/group .
Though not tried on Red Hat, I have seen multiple lines for the same group in /etc/group in a very large unix SVR4 system.

I have seen the same thing:
realgrp::123:user1,user2
dummy1::123:user3,user4
dummy2::123:user5,user6

All six users are in group 123. And when group 123 is translated, it comes out as "realgrp".

We are adding 1000 users having secondary group. After adding 1000 users, Line of secondary group contains 7053 characters.

Is there any way to change LINE_MAX value of OS ???
Currently LINE_MAX value is 2048.

Thanks in advance...

You don't need the dummy group names.
You can have multiple lines for the same group.