Using SSH login without password

Published 10 Feb 2010 Read time 1 min 54 sec(s) (2699 views). Solaris

This is a simple article that provides the necessary steps to allow ssh login without the need of entering the users password

on serverA generate a pair of authentication keys:

user@serverA$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/usera/.ssh/id_rsa): <Enter>
Created directory '/home/usera/.ssh'.
Enter passphrase (empty for no passphrase): <Enter>
Enter same passphrase again: <Enter>
Your identification has been saved in /home/usera/.ssh/id_rsa.
Your public key has been saved in /home/usera/.ssh/id_rsa.pub.
The key fingerprint is:
a1:b2:c3:d4:e5:f6:7a:8b:9c:0d:1e:2f:a3:b4:c5:d6 usera@serverA
The key's randomart image is:

do not enter a passphrase, To generate an SSH1 RSA or SSH2 DSA key pair, specify the -t rsa1 or -t dsa options.

use ssh to create a directory ~/.ssh on serverB and append usera ssh public key usera@serverB:.ssh/authorized_keys and enter the users password one last time:
```
usera@serverA$ ssh usera@serverB mkdir -p .ssh
usera@serverA$ cat .ssh/id_rsa.pub | ssh usera@serverB 'cat >> .ssh/authorized_keys'
```
An alternative on some Linux systems, is to use the ssh-copy-id script to append the public key in the local ~/.ssh/id_rsa.pub file to the ~/.ssh/authorized_keys file on the remote system, for example:
```
usera@serverA$ ssh-copy-id usera@serverB
usera@serverB's password: remote_password
Now try logging into the machine, with "ssh 'usera@serverB'", and check in:

  .ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.
```
When prompted, enter your password for the remote system.

The script also changes the permissions of ~/.ssh and ~/.ssh/authorized_keys on the remote system to disallow access by your group.

Now it's a simple as:

usera@serverA$ ssh usera@serverB
usera@serverB$

Verify that the permissions on the remote ~/.ssh directory and ~/.ssh/authorized_keys file allow access only by you:

usera@serverA$ ssh usera@serverB ls -al .ssh
total 4
drwx------+ 2 usera mygrp   5 Feb 10 15:47 .
drwxr-xr-x+ 3 usera mygrp   9 Feb 10 15:48 ..
-rw-------+ 1 usera mygrp 397 Feb 10 15:48 authorized_keys

NOTE: On some systems you need to place the public key in the file .ssh/authorized_keys2