- What key does what
All the keys do authentication. Except known_hosts
, which is just a list of known hosts and their public host keys.
- what if I have to format / reinstall new os in my system, which files to save(backup)
All of them.
- how is it I'm able to ssh server_2 but unable to access it via filezilla
Probably wrong configuration in FileZilla. You didn't show it to us, so we have no idea to verify what is wrong.
- I've have a passphrase in
key
file, how can I change it
From manual page for ssh-keygen
:
The passphrase can be changed later by using the -p option."
ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
- What if I want to change
server_1.key
server_1.pem
keys just like we change our password
Generate public key from the new one:
ssh-keygen -y [-f input_keyfile]
and replace the old public key in the server's ~/.ssh/authorized_keys