$ ssh-keygen -b 4096

To assign passphrase 

$ ssh-keygen -P "myp@ssword"

To change passphrase of the private key

$ ssh-keygen -p 

To create keys with custom filename

$ ssh-keygen -f my-rsa-key

To add custom comment to the key

$ ssh-keygen -C "This key is for my.server.in"

To change comment of the key

$ ssh-keygen -c

To hash the content of known_hosts file

$ ssh-keygen -H

To delete all the keys related to 192.168.122.101 host from known_hosts file

$ ssh-keygen -R 192.168.122.101

regards,

T.Dhanasekar