Linux problem

[Peter Korsten]

So... I'm co-sysadmin of this Linux machine that hosts a number of web 
sites. It's a stand-alone server, running Centos... something or other.

The problem is that the machine is really busy, and now crashes very 
regularly. That it's busy is not something that we can fix right away 
(we'd have to invest in new hardware, which takes money that we don't 
necessarily have), but why is it crashing? Isn't Unix, and by extension 
Linux, supposed to be stable?

What happens is that some operation in httpd or exim causes a 'null 
pointer' fault in the kernel, and then the whole thing goes. Or some 
mysql query won't finish and takes up all processing time, requiring us 
to do a 'kill -9' on mysqld.

Is there anything simple we can do to solve this problem? My solution 
would be to install Solaris, but you know, that's not my decision to make.

- Peter