How to Set Up Password‑Free SSH Login Between Two Linux Hosts

Assume you are the user "aliceA" on hostA and you want to SSH to hostB as user "aliceB" without typing a password.

First, log in to hostA as aliceA.

Generate an RSA key pair (the keys are stored in ~/.ssh). $ ssh-keygen -t rsa Create the .ssh directory on hostB for aliceB (skip this step if it already exists). $ ssh aliceB@hostB mkdir -p .ssh Copy aliceA's public key to aliceB's authorized_keys on hostB.

$ cat .ssh/id_rsa.pub | ssh aliceB@hostB 'cat >> .ssh/authorized_keys'

After this, ssh from aliceA@hostA to aliceB@hostB will no longer prompt for a password. The whole process can also be done in one step with ssh-copy-id -i ~/.ssh/id_rsa.pub aliceB@hostB.

Troubleshooting

If you are still asked for a password after key authentication is set up, check the system logs (e.g., /var/log/secure ) for errors such as: Authentication refused: bad ownership or modes for file /home/aliceB/.ssh/authorized_keys This usually means the authorized_keys file has incorrect permissions or ownership. Ensure the file is not readable by anyone other than its owner.

$ chmod 700 ~/.ssh/authorized_keys