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In our lab, all the LDAP users are assigned to a group vboxusers whose home directory is present in the server. We are using NFS to mount the home directory of an user to the client machines. I was installing a new client machine and added it to the network. I configured the LDAP in this new machine and strangely there was a group cimsrvr which was assigned the same ID as vboxusers in the remaining client machines.

In the newly installed machine, I find the below entry in /etc/group file.

cimsrvr: 501

In all of the remaining client machines, I find the entry in /etc/group file as,

vboxusers: 501

I was assigning permission to all the users belonging to vboxusers to access Virtualbox. When I assigned the permissions to cimsrvr in the new machine, the vboxusers were able to access Virtualbox without any problem. So, I figured out the group name is just for our understanding and the machine just uses the group ID. That's why all the users belonging to group 501 were able to access VirtualBox.

My question is, how did the cimsrvr group got assigned to 501 in the first place when I did not create any group by that name?

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up vote 3 down vote accepted

The group IDs (the numbers) are arbitrarily assigned when RPMs are installed, unless the package explicitly adds these entries specifying a specific GID number.

Example

From a Fedora 14 system.

$ more /etc/group
vboxusers:x:502:saml
jetty:x:485:
xfs:x:43:
kvm:x:36:qemu
qemu:x:107:

To migrate these groups to another GID you'll have to search the disk for all occurrences and then chgrp <new GID> to move them to some unused number.

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oh ok. So, was I correct in my understanding that the machine looks only for group ID rather than the group name? Because, when I assigned permissions to cimsrvr with group ID 501, I was able to access the Virtualbox application. –  Ramesh Oct 14 '13 at 15:48
1  
The names are essentially just labels for the GID numbers. The numbers are what really matter on the disk, in most cases. There are some situations where the name does matter though. –  slm Oct 14 '13 at 15:51
    
Perfect. I am learning new things each and every day. God, I am starting to love Linux. –  Ramesh Oct 14 '13 at 15:55
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