After an HMC upgrade, sometimes you will lose entries that allow password-less logins to your HMC.
If this happens, run the following commands:
Log on to HMC manually:
mkauthkeys -a “string”
where “string” is the whole ssh key from the remote hosts, e.g. “ssh-rsa asdfasdfasdfasdfasdfasdfasdfasdfaasdfasd= root@nim01”
Should be done!