It’s because your key is encrypted with a passphrase to prevent others from reading it.
The most convenient way of using passphrased keys is by using
ssh-agent to start an authentication agent (which runs in the background):
$ eval "$(ssh-agent)" Agent pid 44304
…and then using
ssh-add to register your key with the agent so that it’s used automatically for subsequent SSH connections:
$ ssh-add ~/.ssh/id_rsa Enter passphrase for /home/khanhpn/.ssh/id_rsa:
You’ll be asked to enter your passphrase when you run
ssh-add, but you won’t need to do so again while
ssh-agent is running.
You can find more information on GitHub. Also note that you’ll have to do this every time you log in, so you might like to add the
eval "$(ssh-agent)" step to your