I want to have a configuration in my Ubuntu system so that if the cpu processing exceeds 90% it gives a beep sound. Is this possible?
Yes. I wrote a script that plays a notification sound when CPU load average exceeds 90% (accounting for all cores).
The system speaker is, by default, disabled on Ubuntu systems, hence using one of the standard notification sound seems a better choice for this.
To run it, simply download the script (save it as notify-highload.sh), and copy to your home directory. Then, from a terminal, run chmod +x ./notify-highload.sh, followed by ./notify-highload.sh -ag &.
If you want it to run every time on start up, add the script to your Startup Applications.
Also, where else can this beep sound be used? like can it be used if the Hard Disk space exceeds 80%.
Yes, it can. I wrote a script available here.
I will add a few more later on.