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Remove a secondary group from user (Linux)

 
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# 1  
Old 07-30-2015
Remove a secondary group from user (Linux)
Oracle Linux 6.6

grid user's secondary groups are asmadmin,asmdba,asmoper and dba

Code:
# id -a grid
uid=638(grid) gid=2000(oinstall) groups=2000(oinstall),2100(asmadmin),2200(dba),2300(asmdba),2301(asmoper)

I want to remove dba as the secondary group for grid and keep the remaining ones.
ie. I want grid user to be part of just asmadmin,asmdba and asmoper secondary groups. What is the quickest way to do this ?
# 2  
Old 07-30-2015
Hello John,

Step # 1: Find out user group identity
Use id command:
Code:
id -nG {user-name}
id -nG tom

Output:
Code:
 sales printer

Step # 2: Remove user from printer group
Use the following syntax:
Code:
 usermod -G {groupname1,groupname2,...} {username}

To keep membership for sales only group (remove user tom from printer group), enter:
Code:
usermod -G sales tom
id -nG tom

Output:
Code:
 sales

Hope this helps. But please try this in a NON-PROD environment first.

Thanks,
R. Singh
This User Gave Thanks to RavinderSingh13 For This Post:
John K
# 3  
Old 07-30-2015
Thanks Ravinder,
Using -a option in usermod, you can easily add the user to another group.In my below example, I added john to asmoper group using -a option as shown below

Code:
# useradd -u 28 -g oinstall -G asmadmin,asmdba john
#
# id -a john
uid=28(john) gid=2000(oinstall) groups=2000(oinstall),2100(asmadmin),2300(asmdba)
#
#
#
# usermod -a -G asmoper john
#
# id -a john
uid=28(john) gid=2000(oinstall) groups=2000(oinstall),2100(asmadmin),2300(asmdba),2301(asmoper)

I was hoping for a similair short command to remove just one group from a user. Using your method,I need to list all the groups I want to keep. It could be confusing if the user belongs to several groups

For eg: If I want to remove secondary group asmadmin from john user, I need to list asmoper,asmdba groups which I want to keep after -G

Code:
# id -a john
uid=28(john) gid=2000(oinstall) groups=2000(oinstall),2100(asmadmin),2300(asmdba),2301(asmoper)
#

# usermod -G asmoper,asmdba john
#
# id -a john
uid=28(john) gid=2000(oinstall) groups=2000(oinstall),2300(asmdba),2301(asmoper)

Last edited by John K; 07-30-2015 at 11:32 AM..
# 4  
Old 07-30-2015
Code:
gpasswd -d user group

Code:
gpasswd -d john asmoper

This User Gave Thanks to Aia For This Post:
John K
# 5  
Old 07-30-2015
If you really have to use usermod, try
Code:
usermod -G$(id -nG john | sed 's/^[^ ]* //;s/asmadmin//;s/  */,/g') john

, assuming the first group listed is the primary group. You may want to define a shell function.
This User Gave Thanks to RudiC For This Post:
John K
# 6  
Old 07-30-2015
Brilliant. Thanks Aia. Thanks Rudic
 
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