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Most of the counter-based tools on Linux systems read statistics from the
/proc file system. /proc is a “pseudo” file system that exists only in kernel
memory and is used primarily for querying various per-process as well as
kernel statistics. The /proc file system is organized as a directory hierarchy,
with the process (a unique integer value assigned to each process) appearing
as a subdirectory below /proc. For example, the directory entry /proc/2155
would contain per-process statistics for the process with an ID of 2155. There
are /proc entries for various kernel statistics as well. In both this chapter and
Chapter 3, we provide programming projects where you will create and access
the /proc file system
