====== Find_&_Remove_an_old_SSH_Key_for_all_users ======

With changing to a new mailserver, we had to revoke individual sshkeys in known_hosts, and add in a default system one instead.

 #!/bin/bash
 # Script to find old ssh keys of mail on oldserver, and to comment them out.
 
 HOSTKEY="ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAl1NYD26bFvDqUVXuVjZuerXA1D4sx3qJ/aT7kN9oc4Z9r8uEYUyiE1ZwyjtrGQY6AZtfVo3qkNzxqpziRrf4uPVYQ+9128bEkpByCx4GGtbBzcbxa5cuRhNpYgQDyK2Dt+P03yq5M2QFmnVJPDOr8Fjf8pImUGawUeYl1XLZwkM="
 
 for user in `ls /home/`
 do
 
        if [[|-f "/home/$user/.ssh/known_hosts" ]]; then
                echo "Doing User Search and Replace for $user"
 
        mv /home/$user/.ssh/known_hosts /home/$user/.ssh/known_hosts.bak
            grep -v "^[[^#]]*\($HOSTKEY\)" < /home/$user/.ssh/known_hosts.bak > /home/$user/.ssh/known_hosts
                chown $user:users /home/$user/.ssh/known_hosts
        fi
 done

"grep -v" was used to select the "inverse" of a search string.