daryl.mu

If you want to harden and secure your SSH installation on Ubuntu Linux then there are a few simple steps you can follow:

1. Remove root access - this should be the highest priority on your list and not just to prevent hackers.  Using a root account to do everyday tasks is a BAD THING and using a root account to ssh onto a server is a VERY BAD THING.

Use a normal account and sudo when you need to play God!

To prevent root access via ssh:
sudo vi /etc/ssh/sshd_config
Find the line that says:
PermitRootLogin yes
and change to:
PermitRootLogin no

2. Reduce the time period that SSH waits for a password. In the same /etc/ssh/sshd_config file there is an entry
LoginGraceTime 120
Reduce this to a more sensible time in seconds, say 30 assuming you have all 10 fingers.

3. Restrict who can ssh onto the machine. In the file /etc/ssh/sshd_config add an entry as follows:
AllowUsers someGuy someOtherGuy
Specifying the users you want to be able to logon separated by spaces.

Once you have completed these steps restart the ssh daemon:
sudo /etc/init.d/ssh restart