Thanks for sharing this!
Here is some information.
In

Code:

ps -eaf

the fourth column is "CPU usage percent".
The "portmapper is not responding" is a system console message. Such a message occurs asynchronously, is not related with your current action. But can be disturbing, so usually you better go to another login screen that is not a system console.
In this case some process on the system (usually an access attempt to NFS, network file system) wants a process "portmap" or "rpcbind" that is not running. You can check that with the "ps -eaf" command, and check its functionality with the "rpcinfo" command.)
But probably this is not important at all, and certainly not relevant for your problem.
Your problem was that you immediately started the backup and that freezes your session. The best thing you can do is wait until the backup is finished and your session continues. Watch the activity light on the tape, and do not interrupt/force-remove the tape!
I guess the backup program puts a /etc/nologin file with a message. Then a user cannot login, and the message is displayed instead. At the end the backup program deletes the /etc/nologin.
If interrupted the /etc/nologin remains.
A # su - userlogin is a good trick - it ignores the /etc/nologin.
Also a # rm /etc/login would have worked.
See this web page.