Linux/Unix Filesystem - Directory Hierarchy

Directory	Description
/	Root of the file system tree.
/bin	“Binary” directory contains certain fundamental utilities like “ls, cp or mv”.
/sbin	“System/superuser binary” directory contains utilities like “init”, usually needed to start, maintain and recover the system.
/etc	Contains system-wide configuration files and system databases. Also ASCII data.
/dev	“Devices” directory contains file representations of peripheral devices and pseudo-devices.
/proc	“Processes” directory contains all process ID and details as files.
/lib	“Essential Libraries” C libraries. On modern systems, contains the shared libraries needed by programs in /bin, and possibly loadable kernel module or device drivers. Linux distributions may have variants /lib32 and /lib64 for multi-architecture support.
/opt	“Optional” directory contains locally installed software.
/var	“Variable” directory, a place for files that may change often - especially in size. Example: Log files.
/usr	“User file system” directory contains user home directories.
/tmp	“Temporary” directory, a place for temporary files.
/lost+found	Contains files deleted by fsck