SSH

Generate OpenSSH key in Mac

1. Run ssh-keygen, or using rsa then run: ssh-keygen -t rsa

   • The SSH key file path is under ~/.ssh directory.
   • You will be prompt enter passphrase, press enter for empty passphrase
   • Upon creation, you will see id_rsa and id_rsa.pub

2. Run cd ~/.ssh, then ls -a

   • It outputs 2 files: id_rsa and id_rsa.pub

3. Adding id_rsa.pub value to the VM you want to SSH-ing

   • Eg: Digital ocean » My profile » Security » Add SSH, paste the value in there.

Remove an old host keys in Mac

• Assume Digital Ocean remote IP is 192.25.25.0, to remove, run below command.

ssh-keygen -R 192.25.25.0
   # old key path: ~/.ssh/known_hosts.old

Define SSH with specific host.

• Under ~/.ssh directory, open config file

Host *
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/key_name_1
  IdentityFile ~/.ssh/key_name_2

SSH working logic for connecting 2 remote hosts

Host A

1. Inside Host A
2. Create key: ssh-keygen -t rsa
3. Above key will be a pair files: .rsa && .pub
4. Copy content from .pub

Host B

1. Inside Host B
2. Go to folder /.ssh
3. Adding authorized_keys file
4. Paste the content from .pub of Host A
5. Done