Is there any way to find out sometimes when the server load is high, what process and what activity cause that ? I have a shared webserver and mailserver (HTTP, DNS, SMTP, IMAP, POP, FTP,...) and sometimes the load is very high. 25-50 or more. How can I find out what cause that, and what can I do to give normal performance continuously ?
Use the command "top" or install htop to see what processes are eating the most of the system's capacity.
I could also go into tools like sysstat (iostat / vmstat / etc.) but using top would be the first thing I'd try.