I have a cPanel server and I need to limit my clients' number of entry processes but my cPanel server doesn't have CloudLinux installed on it.
Is there any way to achieve that without purchasing CloudLinux?
Limit Entry Process is a CloudLinux feature and not a WHM/Cpanel feature therefore you will not find it in other Linux distributions, it happens to be one of CloudLinux's best selling points.
Either buy CloudLinux or learn how to throttle using a range of apps and setup configurations, plently on Google.