SSH Without a Password

The following steps can be used to ssh from one system to another without specifying a password.

Notes:

• The system from which the ssh session is started via the ssh command is the client.
• The system that the ssh session connects to is the server.
• These steps seem to work on systems running OpenSSH.
• The steps assume that a DSA key is being used. To use a RSA key substitute 'rsa' for 'dsa'.
• The steps assume that you are using a Bourne-like shell (sh, ksh or bash)
• Some of this information came from:
  http://www.der-keiler.de/Mailing-Lists/securityfocus/Secure_Shell/2002-12/0083.html

Steps:

1. On the client run the following commands:

   $ mkdir -p $HOME/.ssh
   $ chmod 0700 $HOME/.ssh
   $ ssh-keygen -t dsa -f $HOME/.ssh/id_dsa -P ''
   

   This should result in two files, $HOME/.ssh/id_dsa (private key) and $HOME/.ssh/id_dsa.pub (public key).

2. Copy $HOME/.ssh/id_dsa.pub to the server.

3. On the server run the following commands:

   $ cat id_dsa.pub >> $HOME/.ssh/authorized_keys2
   $ chmod 0600 $HOME/.ssh/authorized_keys2
   

   Depending on the version of OpenSSH the following commands may also be required:

   $ cat id_dsa.pub >> $HOME/.ssh/authorized_keys
   $ chmod 0600 $HOME/.ssh/authorized_keys
   

   An alternative is to create a link from authorized_keys2 to authorized_keys:

   $ cd $HOME/.ssh && ln -s authorized_keys2 authorized_keys
   

4. On the client test the results by ssh'ing to the server:

   $ ssh -i $HOME/.ssh/id_dsa server
   

5. (Optional) Add the following $HOME/.ssh/config on the client:

   Host server
            IdentityFile ~/.ssh/id_dsa
   

   This allows ssh access to the server without having to specify the path to the id_dsa file as an argument to ssh each time.

Helpful manpages:

• ssh(1)
• ssh-keygen(1)
• ssh_config(5)