I've got a single web application running on one server. All customers use that one application and little else. I have to work out how much memory each demonstration of httpd occupies. By doing this I'll understand how much ram my new server will require for X customers.

the ps -aux command provides me with % of memory used. I just read online that's % has run out of "available memory". Exactly what does "available memory" mean to linux?

I discovered several articles that explain what not calculate memory usage in linux however i couldn't locate one that will train how calculate just how much memory each httpd needs. Please assist.

The %MEM area in ps is referred to thus within the ps guy page:

%MEM ratio from the process's resident set size towards the physical memory around the machine, expressed like a percentage.

Calculating the memory needed by each httpd process isn't straightforward - it'll highly rely on your webapp itself. httpd processes will even share quite a lot of memory with one another.

The easiest way is to test. Perform tests with various amounts of customers making use of your webapp concurrently (eg. 5 customers, 10 customers, 20 customers) and sample the used memory (in the first number around the -/+ buffers/cache: line within the creation of the free command). Plot the outcomes, and you ought to have the ability to extrapolate to bigger amounts of customers.