The Filesystem Hierarchy Standard (FHS) is a collaborative document that defines the names and locations of many files and directories in a operating file system
The FHS document is the authoritative reference to any FHS-compliant file system, but the standard leaves many areas undefined or extensible. The complete standard is available at http://www.pathname.com/fhs
|contain file system entries which represent devices that are attached to the system.
|is reserved for configuration files that are local to the machine. No binaries are to be put in /etc/. Any binaries that were once located in /etc/ should be placed into /sbin/ or possibly /bin/
|should contain only shared libraries that are needed to execute the binaries in /bin/ and /sbin/. These shared library images are particularly important for booting the system and executing commands within the root file system.
|The /mnt/ directory is for temporarily mounted file systems, such as CD-ROMs and floppy disks.
|presents information about processes and other system information
|stands for universal system resources
More, see wiki/Unix_filesystem