ssh without a password

Sometimes you need to be able to ssh to a server without giving it a password; say, if you have an automated process that writes files and copies them to a server. I had to set this up quite a few times recently - here's the recipe I followed (this assumes that the permissions on your various ~/.ssh directories are correct)

You'll need:

• a client: a computer from which you'll ssh to another
• a server: the computer to which you'll ssh from a client

Then,

• on the client, run 'ssh-keygen -t rsa' to generate ~/.ssh/id_rsa.pub and associated files. When asked for a password, just hit Enter. You need to generate id_rsa.pub only once per client - you can reuse it for each of the servers.
• scp ~/.ssh/id_rsa.pub server:~/.ssh/client.pub
• ssh server
• supply your password to get in
• cd ~/.ssh
• cat client.pub >> authorized_keys
• if this creates a new authorized_keys file, change its permissions to 600: chmod 600 authorized_keys
• log out of the server & try to ssh to it - you should get in without having to specify a password
• of course this is less secure than ssh with a password, so use it wisely and sparingly
• your mileage may vary - some installations may require a file named authorized_keys2; the above recipe works for me in my environment.