I‘m using a Mac OS X and combination of ssh-agent+ssh-add to adds RSA or DSA identities to the authentication agent. ssh-agent provides me a secure way of storing the private key. However, I’d like to expire identities added to the agent within half an hour. How do I set lifetime of identities added to the agent under Unix / Linux / BSD / Apple OS X operating systems?
Recently, my desktop hard disk crashed. So I reinstalled Linux and created a new set of private RSA keys for authentication. However, two of my remote UNIX servers still uses old DSA keys. I do not remember root password for those servers. I do have backup of private and public DSA keys and currently stored in /backup/home/user/.ssh/id_dsa and /backup/home/user/.ssh/id_dsa.pub. How do I force my ssh clients to use identity file /backup/home/user/.ssh/id_dsa to get back to my remote UNIX servers?