UNIX for Dummies Questions & Answers

Hi all


usermod -G Group_id login

it is replacing the existiong Secoundry groups and is adding the only group speced in usermod command

how can we retain the existing secoundry groups and add a user to a new group

The lack of an 'add' option has always bugged me too.

You can specify more than one group with -G, i.e. -G group1,group2,group3 but you'll have to extract group information somehow to get their previous groups.

Closest I've gotten to that is

Code:

egrep 'user[^:]+$' /etc/group |
        sed 's/:.*//' |
        xargs echo |
        sed 's/ /,/g'

which feels like a horrible hack for something one feels ought to be built into something else..

Well, to be honest, I simply edit the /etc/group file, usermod or no usermod.

Is this a reccomended practice? It's less dangerous than editing /etc/passwd, I suppose, but could still really mess up your system if you aren't careful. It's not something you can do from a script file, either.

It may not be a recommended practice, but it is nowhere as dangerous as fiddling with /etc/passwd. Another thing, about the scripting bit. If you really want to put things into a script, look at 'ex'. I use it quite often to edit whole bunches of files, esp. on connections where I can't use vi due to the lack of proper terminal settings.

And about that hack, why not use the 'id' command? 'id -a' gives you all the info about the current user groups. You could run that, or some similar options, and pass that through sed to get the current list of groups, which you could use in the 'usermod -G' command. (Can't give any examples, no access to unix right now...)

Much better.

Code:

id -G | sed 's/ /,/g'

You are lucky that Linux allows '-G' with the id command. On Solaris, its not as smooth.

Code:

id -a <username>|cut -d"=" -f4|tr -d '[0-9]()'