Master SSH Key Authentication: Generate, Deploy, and Use ssh-agent

You can configure SSH to use key‑based authentication instead of username/password by generating a public‑private key pair.

Environment: Two virtual machines – workstation (client) and servera (server). The goal is to SSH from workstation to servera using keys.

On workstation run ssh-keygen to create the key pair, optionally setting a passphrase.

[it@workstation ~]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/it/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/it/.ssh/id_rsa.
Your public key has been saved in /home/it/.ssh/id_rsa.pub.
...

id_rsa is the private key and id_rsa.pub is the public key.

Upload the public key to the server with ssh-copy-id :

[it@workstation ~]$ ssh-copy-id -i .ssh/id_rsa it@servera
...
Number of key(s) added: 1

Now connect with ssh ; you will be prompted for the private‑key passphrase.

[it@workstation ~]$ ssh it@servera
Last login: Thu Oct 29 14:41:13 2020 from 10.10.10.20

To avoid entering the passphrase each time, start ssh-agent and add the key:

[it@workstation ~]$ eval $(ssh-agent)
Agent pid 3191
[it@workstation ~]$ ssh-add .ssh/id_rsa
Enter passphrase for .ssh/id_rsa:
Identity added: .ssh/id_rsa ([email protected])

After adding, subsequent ssh commands reuse the cached credentials in the same shell. In a new shell you must add the key again. The same steps can be repeated for other servers such as serverb .