Linux command to kill all MySQL sessions from a specific User?
Try this :

mysql -uuser -ppassword -e 'show processlist' | grep USER_NAME | awk {'print "kill "$1";"'}| mysql -uuser -ppassword


The command will list the processes running in the database and return a kill 'query id'; command and pipe it into mysql again.
 Be carefull with this command as there is no rollback form it :)