Caching uses *more* RAM. The idea is that unused RAM is wasted. It's better to use it to cache data so that you don't need to hit the disk (or if you're caching precomputed data, don't need to hit the CPU).

Why not just create an account for each user and make each of them own their own files? It's pretty easy these days to chroot user accounts and give them only SFTP access (no shell), since recent versions of the openSSH server include that functionality by default.



apt-get install php-apc && /etc/init.d/apache2 restart

That will make Apache use 10-20MB more RAM, but your PHP scripts will run nearly twice as fast.

Also don't forget the various caching plugins that are available for popular PHP programs (e.g. wp-super-cache for Wordpress). These plugins usually don't cause increased memory usage, as they use static files instead of RAM.

That seems like the best option for me, I'll have to try that (not only VPS but also a linux newbie ).

After installed php-apc, now when I run free -m +- buffers/cache is now 288 free, and before that it was 265, so it looks like I got 20 mb ram back Anyway, everything works fine, my sites are loading fast, all the trouble setting everyting up is now paying off, linode is really great!

Couple more questions:

- I see that many people are using lighttpd and not apache. Whats the difference or in what situations is better to have it then apache?

- linux installation, I've chose Ubuntu 9.10, is there a difference in memory usage with some other version?

You got 20MB back is because you restarted Apache. Make a few visits to your site and the memory usage will return to where it was, plus a few more MB for the APC cache.

1) Apache with mod_php handles both static (html, css, images) and dynamic (PHP) requests using the same pool of processes. lighttpd (and nginx, which has recently become more popular) separate them. Static files are served by a preconfigured number of worker processes, and memory usage stays nearly constant whether you have 100 visitors or 10000 visitors. PHP requests are passed to a separate pool of FastCGI processes, which runs with its own set of privileges and keeps memory usage nearly constant. You can see why people say lighttpd and nginx are good for memory-constrained VPS's. The drawback? If you want to use mod_rewrite (pretty URLs) with your favorite CMS, you'll have to put the rules into the server configuration itself, rather than in a convenient .htaccess file. Works fine if it's just your site, but not so good when you have clients constantly complaining about their .htaccess files not working.

2) As long as you stick to 32-bit, memory usage difference between different distributions is generally negligible (a few MB).

Thank you!