Keyless ssh / ssh-keygen: setup and gotchas

If you ssh into a server a lot, you'll get tired of typing in your password over and over again pretty quickly. Fortunately, you can generate a set of public and private keys on your local client machine, place the public key on the server, and ssh without having to enter a password. Here's how.

1) Generate your keys
    jknight@localmachine:~$ ssh-keygen -t rsa    (generate an rsa key)
    Generating public/private rsa key pair.
    Enter file in which to save the key (/home/jknight/.ssh/id_rsa):
    Created directory '/home/jknight/.ssh'.
    Enter passphrase (empty for no passphrase):
    Enter same passphrase again:
    Your identification has been saved in /home/jknight/.ssh/id_rsa.
    Your public key has been saved in /home/jknight/.ssh/id_rsa.pub.
    The key fingerprint is:
    1f:bf:a8:1f:bf:a8:1f:bf:a8:1f:bf:a8:1f:bf:a8:1f jknight@localmachine
    jknight@localmachine:~$

2) Find the keys you just created in your home .ssh directory
    jknight@localmachine:~$ cd .ssh   (go into the new .ssh directory you just created)
    jknight@localmachine:~/.ssh$ ls    (look for your 2 keys: one private and one public)
    id_rsa  id_rsa.pub

3) Use scp to put your public key on the server
    jknight@localmachine:~/.ssh$ scp id_rsa.pub remoteUserName@remoteserver.com:~/
    The authenticity of host 'remoteserver.com (192.168.1.3)' can't be established.
    RSA key fingerprint is 65:fe:34:65:fe:34:65:fe:34:65:fe:34:65:fe:34:65.
    Are you sure you want to continue connecting (yes/no)? yes
    Warning: Permanently added 'remoteserver.com,192.168.1.3' (RSA) to the list of known hosts.
    remoteUserName@remoteserver.com's password:
    id_rsa.pub                                                                                                                                100%   

4) ssh on to the server to put your public key in the right place
    jknight@localmachine:~/.ssh$ ssh -l remoteUserName remoteserver.com
    remoteUserName@remoteserver.com's password:
    Linux remoteserver 2.6.17-11-generic #2 SMP Fri May 18 22:25:27 UTC 2007 x86_64

5) Add your public key to the authorized_keys file on the server in the hidden .ssh directory
    remoteUserName@remoteserver:~$ mkdir .ssh    (if the .ssh directory doesn't exist, create it)

    (now for the important steps: ADD your public key to the authorized_keys file ...)
    remoteUserName@remoteserver:~/.ssh$ cat id_rsa.pub >> .ssh/authorized_keys
   
    (finally, the big 'gotcha': make sure permissions are correct on the authorized_keys file)
    remoteUserName@remoteserver:~/.ssh$ chmod 600 authorized_keys

6) All set?
    Open a shell on your local machine, and you should now be able to ssh without typing in a password
    jknight@shadowbox:~/.ssh$ ssh -l remoteUserName remoteserver.com
Linux galadriel 2.6.17-11-generic #2 SMP Fri May 18 22:25:27 UTC 2007 x86_64
   success!

Notes
These are all equivalent ways to ssh to a server:
ssh -l remoteUserName remoteserver.com
ssh -lremoteUserName remoteserver.com
ssh remoteUserName@remoteserver.com

scp syntax can take some getting used to.  To put a file out to a server use the following. You can specify the target file name, or just the directory:
scp /local/path/file.txt remoteUserName@remoteserver.com:/remote/server/path/
scp /local/path/file.txt remoteUserName@remoteserver.com:/remote/server/path/out.txt
To get a file from a remote server, use:
scp remoteUserName@remoteserver.com:/remote/server/path/file.txt /local/file/path