How can I use a private key in an ssh client for only one host?

Question

I'm using Ubuntu. How can I use a private key in an ssh client for only one host? The private key is used for all hosts, every time I connect to any server, the private key authentication is used.

Answer 1

You need to create or edit your SSH configuration file at ~/.ssh/config.

For all the details, check man ssh_config. But basically, it consists of several entries like this:

Host example
    Hostname example.com
    User quber
    IdentityFile ~/.ssh/my_idfile

A Host line introduces each host, and the following lines are indented. The name on the Host line is a nickname (you will type ssh example instead of ssh [email protected].) If you don't want to use a nickname, you can use the full hostname:

Host example.com
    User quber
    IdentityFile ~/.ssh/my_idfile

Now ssh will automatically use the specified username and private key for this host, and only this host.

If you don't want the private key to be used for other hosts, make sure it is not named id_dsa, id_rsa, or the other files which are used by default for all hosts (the whole list is in man ssh). Give it a unique name, perhaps pertaining to the host it's for.