SSH and DNS reverse lookup

One of the sucking thing with SSH is that it uses DNS to map IPs to domain name.
When you have some DNS problems and need to connect through SSH into a box, you can get some timeout or delay.

This is almost true in ESX servers. To solve this on ESX 3.0.2 you need to create a file : /etc/sysconfig/sshd with this inside :
OPTIONS="-u0"
then restart your SSH daemon (don’t worry, you will not loose your connexion if you didn’t make a mistake).

Under debian like system, you only need to add this line in the /etc/ssh/sshd_config : UseDNS no
then restart your SSH daemon.

Disconnect a user from Linux systems

Sometimes you may like to disconnect a user who forgot an open SSH session on a server.
I use this to do it : kill -HUP
And you ?

We can also set an idle time to automatically close sessions…