Under linux, there is a special filesystem mounted under /proc that gives access to the linux kernel settings and information.
Some of the information you can find includes:
Also, the root user can change some kernel settings by writing to particular values. For example, to allow your linux machine to act as a router by forwarding packets from other machines, it is necessary (but often automatic) to do "echo 1 > /proc/sys/net/ipv4/ip_forward".
Writing programs that get information from /proc is a good way to make them non-portable to other unix(-like) systems.
See also ProcessNotes, procinfo(8), proc(5).
One page links to ProcFileSystem:
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