Login to a Linux/Unix System without a password
Setting up SSH/RSH Keys for Remote Administration Under Linux/Unix can be one of the most time saving things you can do. I've set this up because I am managing a dozen Linux based kiosks based Lubuntu Linux and Mozilla FireFox on that need to remotely shutdown and startup.
For managing the kiosks I am using Ubuntu 12.04 LTS, on a VLAN network. This server also remotely shuts down some Windows based stations and is used for Imaging using the FOG project. I need to update the RSH Public and Private Key because I have replaced the server.
Setting up RSH Public and Private keys are trivial but this allows me to control the systems without having to enter a password every time I want to do something to the computer (besides something that requires root privileges).
The first thing I do on the computer I want to control the other computers with is generate a public and private key. I've done this in a .ssh directory using the Terminal
$ mkdir -p $HOME/.ssh
$ chmod 0700 $HOME/.ssh
$ ssh-keygen -t dsa -f $HOME/.ssh/id_dsa -P ''
This should create two files, $HOME/.ssh/id_dsa (private key) and $HOME/.ssh/id_dsa.pub (public key).
In my case I'm using a script called dafturn-ofris which is kind of a steady state script for linux which prevents users from making changes to the system and rebooting restores the system to the state it was frozen in. So I unfreeze the client system (the system I want to control remotely) and copy the public key from the "Server" to the client; I used SCP to accomplish this.
On the computer you created the key on open the Terminal move to the directory you generated the public key. In my case it is the .ssh folder in the $HOME directory of the user I'm logged in as.
$ scp id_dsa.pub username@remotehost:directory/to/save/it/in/
Enter in your password and this will complete the file copy.
Then login the remote client move into the directory where you saved the public key and run the following commands.
$ cat id_dsa.pub >> $HOME/.ssh/authorized_keys2
$ chmod 0600 $HOME/.ssh/authorized_keys2
Depending on the version of OpenSSH your using 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; your choice.
$ cd $HOME/.ssh >> ln -s authorized_keys2 authorized_keys
Now you should be able to remote into the client computers you want to control from the server computer without being prompted for a password; with the exception of root access. I use this for running rsh command that remotely shuts down client stations when its closing time.
Source Credit: http://csua.berkeley.edu/~ranga/notes/ssh_nopass.html
