Removing a user that doesnt exist from a group

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# 1  
Old 07-26-2011
Removing a user that doesnt exist from a group

Hi there, normally if I want to remove a user tht I have added to a specific group, i would do the following

this is what my group2 looks like

# grep group2 /etc/group

user1 has been defined in a few groups

# id -nG user1
group1 group2 group3

So this is the situation, on a large number of boxes, some local accounts (like user1) have been removed manually from the passwd/shadow files. This subsequently does not clean up the groups that the user may have been in

As far as i understand, to remove a user from a group, I need to define (using usermod) the groups it is a member of and it will go and remove from all those that I havent defined

so to remove the user from group2, issue the command:

# usermod -G group1,group3 user1

However, because the user doesnt exist i get

id: user1: No such user

Is there any way I can use a utility to clean this up or will I have to hack the file ?

any help would be greatly appreciated
# 2  
Old 07-26-2011

Test if next command can be useful for you:
$ gpasswd -d user group

# 3  
Old 07-26-2011
Methinks that running the unix commands "pwck" and "grpck" before you start would be wise.

so to remove the user from group2, issue the command:
# usermod -G group1,group3 user1
This command is incorrect. The "-G" defines the primary group. A user cannot have more than one primary group. This is academic anyway because the user has been removed "manually" from /etc/passwd and /etc/shadow therefore cannot be referred to by name (hence the error message).

Where relevant to your Operating System be sure that the "pwconv" command was run after a manual edit to /etc/passwd (which used "vipw" not "vi" we hope).

As no command now can refer to the deleted users by name the only possible repair is to use an editor to repair the Group file.
Obviously copy the /etc/group file before editing the file and use the unix command "grpck" before and after to check the Group file for inconsistencies.

Last edited by methyl; 07-26-2011 at 08:34 PM.. Reason: assorted typos and additions
# 4  
Old 07-28-2011
thanks all, the gpasswd command worked perfectly and methyl, thanks, you are right i should run pwck and grpck before hand, however you are wrong about the 'usermod -G' command above as that works perfectly well. I believe -G is for suplimentary groups not primary so all is good. The man page confirms this ...

-G, --groups GROUP1[,GROUP2,...[,GROUPN]]]
  A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma .............

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