How to check for free ports on Linux Box

[Bruno Wolff III]

On Wed, Sep 20, 2006 at 15:50:38 +0530,
  Kaushal Shriyan <kaushalshriyan at gmail.com> wrote:
> 
> I need my apache web server to listen to a particular port, On my box
> there are 100 of applications which uses port to run
> 
> My Query is how do i check for FREE PORTS on my box, is there any
> utility where i can find FREE Ports and use it for my application(Apache Web
> Server)

This doesn't make much sense. If you need apache to listen on a particular
port then it needs to listen on that port and there isn't any reason to
be checking other ports.
What you might want to do is see if anything else on the system is using
that port. Looking at /etc/services is a quick way to look for potential
conflicts. It will tell which ports are typically used by which services.
You can also run netstat and look for sockets in a LISTEN state to see which
ones are actually being used on your system at a given time.