Unable to remove user: "user is currently logged in"

SU to the user su - username and run kill -9 -1 as the user.

Exit the shell and try the userdel -r username again.

Or you can check for processes from the user using lsof -u username and kill the relevant PIDs.

Or pkill -u username or pkill -u uid

Or ps aux | grep <username> and kill the processes the user is running.

If the above steps don't help! (Assuming you are using on the runlevel 5)

You could try the following:

1. Change the runlevel to 3 (init 3)
2. log-in with other than deleting account to delete (root/other account)
3. userdel -r username

I try the steps to del the user1

1. su user1

2. kill -9 -1

3. su

4. sudo deluser user1