When you need to ssh to server without entering password.

Loggin into server without password is stupid way. But sometime we need to do that e.g. Cron

So

# CREATE DSA AT CLIENT
user1@client:~$ ssh-keygen -t dsa

Generating public/private dsa key pair.
Enter file in which to save the key (/Users/user1/.ssh/id_dsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /Users/user1/.ssh/id_dsa.
Your public key has been saved in /Users/user1/.ssh/id_dsa.pub.
The key fingerprint is:
9a:30:11:3c:3c:cf:89:01:3a:e1:5d:bd:49:c9:50:f4 user1@client
The key's randomart image is:
+--[ DSA 1024]----+
|. .+.o*o. |
|.o. B. =. |
|o. ..B..oE |
| . ..+o |
| o S |
| o o |
| o |
| |
| |
+-----------------+

# COPY PUBLIC DSA TO SERVER

user1@client:~$ scp ~/.ssh/id_dsa.pub user1@some.server.com:/home/user1/.ssh

user1@some.server.com's password:
id_dsa.pub 100% 642 0.6KB/s 00:00


# SETUP AUTHORIZED_KEY FROM CLIENT TO SERVER
user1@some.server.com:~$ cd ~/.ssh
user1@some.server.com:~$ touch authorized_keys
user1@some.server.com:~$ chmod 600 authorized_keys
user1@some.server.com:~$ cat id_dsa.pub >> authorized_keys


DONE!