Exadata X5 PDU - CLI already in use
Exadata X5-2 and X4-8B racks are delivered with the “Enhanced” PDU metering units connected via the Cisco switch. Although the documentation says they should have static addresses, they don't. You need to configure them manually using serial console connection, this is described in my earlier post here.
However if you forget to exit the serial console connection to the PDU and then try to login using SSH later you'll get the following message:
login as: admin firstname.lastname@example.org's password: CLI already in use!!! Please try again later .....
Then someone has to go all the way to the data centre and reset the PDU or exit from the serial console.