I am working on SLES11 and noticed a strange thing. Whenever I try to swap a user's primary group to become it's secondary group, and assign a new primary group with usermod, it does not change. Only the primary or the secondary changes.


I am using -g and -G in the same command.

If I run the same command twice, the work is done.

Just curious if anyone knows why.

It is because the default behaviour of -G is to add the group that follows it so if you are not mentioning the existing group then it will remove the group already assigned to that user.

For example if the user test is the member of test group and I run the command usermod -G manager test. This will make the test member of manager group. However, it will remove test from the membership of test group. To overcome this you can use -a with -G switch which will append the group.

As you said it works when you run the command second time because in the same command that group is mentioned along with the new group that you want to add.

Just concatenate the commands if you want to get it done in a single line ;-)