"All modern operating systems are able to run many programs at
the same time. For example, a typical Linux server might include a
Web server, an email server, and probably a database service. Each
of these programs runs as a separate process. What do you do if one
of your services stops working? Here are some handy command-line
tools for managing processes.
"Each process uses time on a system's CPU, as well as other
system resources such as memory and disk space. If a program goes
wrong, it can start to use too much CPU time or memory and so deny
other programs the resources they need to run..."