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?
The cron and at services are used to allow commands to be executed at a later time. How do I restrict them to selected users such as root, opt1, opt2 and so on? How do I make sure user php can run php script but cannot modify or install a new job?