09 Jan 2008 SSH Without a Password

Posted by Hans-Henry Jakobsen

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)
• You should consider the security risks before implementing this feature

Steps:

1. On the client run the following commands:

2. $ mkdir -p $HOME/.ssh

4. $ chmod 0700 $HOME/.ssh

5. $ ssh-keygen -t rsa -f $HOME/.ssh/id_rsa -P ''

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

6. Copy $HOME/.ssh/id_rsa.pub to the server.
7. On the server run the following commands:

8. $ cat id_rsa.pub >> $HOME/.ssh/authorized_keys2

9. $ chmod 0600 $HOME/.ssh/authorized_keys2

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

$ cat id_rsa.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

10. On the client test the results by ssh’ing to the server:

11. $ ssh -i $HOME/.ssh/id_rsa server

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

    Host server
    IdentityFile ~/.ssh/id_rsa

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

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Tags: ssh

Filed in Linux, Network