Remote server SSH login without password

SSH login without password

You want to use Linux and OpenSSH to automate your tasks.

Therefore you need an automatic login from host 172.19.7.xyz / user root (user of first server) to Host 172.19.7.acb / user root(user of second server). We don't want to enter any passwords, because we want to call ssh from a within a shell script.

How to do it

First log in on172.19.7.xyz as user root and generate a pair of authentication keys. Do not enter a passphrase:

Server01:~> ssh-keygen -t rsa

Generating public/private rsa key pair.

Enter file in which to save the key (/home/a/.ssh/id_rsa):

Created directory '/home/a/.ssh'.

Enter passphrase (empty for no passphrase):

Enter same passphrase again:

Your identification has been saved in /home/a/.ssh/id_rsa.

Your public key has been saved in /home/a/.ssh/id_rsa.pub.

The key fingerprint is:

3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 a@A

Now use ssh to create a directory ~/.ssh as user root on 172.19.7.abc. (The directory may already exist, which is fine):

Server01:~> ssh root@172.19.7.abc mkdir -p .ssh

Server02's password:

Finally append a's new public key to root@172.19.7.abc:.ssh/authorized_keys and enter Sever02's password one last time:

Server01:~> cat .ssh/id_rsa.pub | ssh root@172.19.7.abc 'cat >> .ssh/authorized_keys'

Server02's password:

From now on you can log into 172.19.7.abc as root from 172.19.7.xyz as a without password:

Server01:~> ssh root@172.19.7.abc

A note from one of our readers: Depending on your version of SSH you might also have to do the following changes:

Put the public key in .ssh/authorized_keys2

Change the permissions of .ssh to 700

Change the permissions of .ssh/authorized_keys2 to 640