Lets say you want to copy between two hosts host_src and remote_machine. host_src is the host where you would run scp, ssh or rsyn, irrespective of the direction of the file copy.
- On host_src, run this command as the user that runs scp/ssh/rsync$ ssh-keygen -t rsaThis will prompt for a passphrase. Just press the enter key. If you assign a password to the key, then you’ll need to enter it each time you scp. It will then generate a private key and a public key. ssh-keygen shows where it saved the public key. This is by default ~/.ssh/id_rsa.pub:
Your public key has been saved in <your_home_dir>/.ssh/id_rsa.pub
- Transfer the id_rsa.pub file to host_dest by either ftp, scp, rsync or any other method.
- On remote_machine, login as the remote user which you plan to use when you run scp, sshor rsync on host_src.
- Copy the contents of id_rsa.pub to ~/.ssh/authorized_keys
$ cat id_rsa.pub >>~/.ssh/authorized_keys
$ chmod 700 ~/.ssh/authorized_keys
If this file does not exists, then the above cat command will create it. Make sure you remove permission for others to read this file via chmod. If its a public key, why prevent others from reading this file? Probably, the owner of the key has distributed it to a few trusted users and has not placed any additional security measures to check if its really a trusted user.
Optional – allowing root to ssh:
- ssh by default does not allow root to log in. This has to be explicitly enabled on remote_machine. This can be done by editing /etc/ssh/sshd_config and changing the option of PermitRootLogin from no to yes.
- Don’t forget to restart sshd so that it reads the modified config file.
- Do this only if you want to use the root login.
Thats it. Now you can run scp, ssh and rsync on host_src connecting to remote_machine and it won’t prompt for the password. Note that this will still prompt for the password if you are running the commands on host_dest connecting to host_src. You can reverse the steps above (generate the public key on remote_machine and copy it to host_src) and you have a two way setup ready!