SSH Without a Password

Submitted by rmiddle on Sun, 07/06/2008 - 11:51

SSH Without a Password

http://www.csua.berkeley.edu/~ranga/notes/ssh_nopass.html

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)

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Category Tags
Linux ssh