Linux server authentication without password using nautilus :
If you are facing problem for sftp, if it asks for password every time when you try to login to the server using sftp in nautilus, you should add your public key file as authorized_keys on the server.
To do this

# scp ~/.ssh/id_dsa.pub 192.168.xx.xx:~/.ssh/authorized_keys

If yu are using RSA keys

# scp ~/.ssh/id_rsa.pub 192.168.xx.xx:~/.ssh/authorized_keys

where 192.168.xx.xx is IP of the server.

Now if you will try to log into server in nautilus using sftp, it will not ask password.