Linux Limit CPU Usage Per Process

Install cpulimit

Type the following commands to install latest stable release:
# cd /tmp
# wget 'http://downloads.sourceforge.net/cpulimit/cpulimit-1.1.tar.gz'
# tar -zxvf cpulimit-1.1.tar.gz
# cd cpulimit-1.1
# make
# cp cpulimit /usr/local/sbin/
# rm -rf cpulimit*

To limit CPU usage of the process called firefox to 30%, enter:

# cpulimit -e firefox -l 30

To limit CPU usage of the process to 30% by using its PID, enter:

# cpulimit -p 1313 -l 30

To find out PID of the process use any of the following:

# ps aux | less
# ps aux | grep firefox
# pgrep -u vivek php-cgi
# pgrep lighttpd

You can also use absolute path name of the executable, enter:

# cpulimit -P /opt/firefox/firebox -l 30

Where,

-p : Process PID.
-e : Process name.
-l : percentage of CPU allowed from 0 to 100.
-P: absolute path name of the executable program file.