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 SuperUser can change some Kernel settings by writing to particular files. For example, to allow your Linux machine to act as a router by forwarding packets from other machines, it is necessary (but usually already automated) 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:
One page links to ProcFileSystem:
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