Common UNIX directories

Directory	Purpose
/etc	System configuration files are stored here.
/bin	This directory holds binaries that must be accessible at all times and that ordinary users are likely to run.
/sbin	This directory is similar to /bin, but these binaries are likely to be used only by the system administrator.
/lib	Critical library files reside here.
/boot	This directory holds system boot files. These files may include the kernel, the boot loader, and similar files.
/usr	This directory tree holds extended system files, including its own /usr/bin, /usr/sbin, and /usr/lib directories. These files aren't necessary for basic system operation, but they may include program files for word processors, Web browsers, graphics programs, server programs, and other tools important to users.
/usr/local	This directory tree holds locally compiled programs in a directory that can be protected from package-management tools or system reinstallation.
/opt	Third-party commercial applications typically reside in this directory.
/var	System files of a transient or variable nature reside here, such as log files, mail queues, and databases.
/home or /users	Each user receives a separate subdirectory of this directory as a home directory.
/root	This directory is the root user's home directory.
/tmp	This directory is temporary "scratch space" for all users.
/mnt or /media	These directories or their subdirectories hold removable media, such as DVD-ROMs or flash disks, although some systems place removable media elsewhere.
/dev	UNIX device files reside in this directory, enabling programs to access hardware devices.

It isn't comprehensive, but it covers the most important directories that exist on most UNIX systems. Some of these directories can be separated into their own volumes. However, some—in particular, /etc, /bin, /sbin, /lib, and /dev—should never be placed on separate volumes. UNIX relies on the contents of these directories to perform critical tasks, including mounting other volumes. For instance, the mount command is likely to reside in /bin, and /dev holds the device files needed to mount a volume. (Some UNIX variants create a dynamic /dev file system, so it may be a separate file system but not a separate volume.)