Change user’s uid/gid

This can be useful when dealing with NFS shares.

How to change

If you’re lucky, it can be as simple as running the following as root:

usermod -u $uid -g $gid $user

The problem is that you can only change the UID if the user has no processes running. This proves difficult with systemd and ssh’ing into the machine with that user.

Cool solution

Use the at command. This command can run schedule the execution of a command. I recommend scheduling the usermod command to 5 mins into the future and then shutting down that machine. Then you just have to wait 6 or 7 minutes with machine off and turn it back on again:

sudo at "+5 minutes"
/use/sbin/usermod -u $uid -g $gid $user

Note: you need to use the full path of the executables here.

File owners

The usermod command only takes care of changing the UID and GID of files in the user’s home directory. I recommend using find to fix any missed files.

find / -uid $old_uid -exec chown -h $new_uid {} +
find / -gid $old_gid -exec chgrp -h $new_gid {} +