Netcat, or nc, is an excellent tool for linux. One thing it's great for is port scanning.

Let us say we want to scan for open ports from 1 to 1000, we can do that like so:

nc -n -z -w 1 192.168.1.2 1-1000

-n prevents DNS lookup. -z will prevent Netcat from receiving any data. -w 1 sets the timeout to 1 second.

You can also use -v to make it verbose, but this will obscure the visibility of successful attempts, which running it without shows.

An example output for the above command is:

Connection to 192.168.1.2 80 port [tcp/] succeeded!

Connection to 192.168.1.2 427 port [tcp/] succeeded!

Connection to 192.168.1.2 515 port [tcp/*] succeeded!

So useful!