userdel: user is currently logged in

userdel: user `username` is currently logged in

If you are trying to remove / delete a user 

# userdel username

and it shows following warning

userdel: user `username` is currently logged in

Now you are not able to remove the user.

Solution :

Run following command.

# pgrep -u username

In place of word username, put your username which is giving you trouble.
Now kill the instances using

# killall -u username

Now try to delete your user but you are still getting same message, check again

# pgrep -u username

You can't run delete user command successfully until you get the instances of the same user using pgrep command.
The result of pgrep command should be blank, No result.