Root Directory - Multiple Root Directories

Multiple Root Directories

Unix abstracts the nature of this tree hierarchy entirely and in Unix and Unix-like systems the root directory is denoted by / sign. Though the root directory is conventionally referred to as /, the directory entry itself has no name—its name is the "empty" part before the initial directory separator character (/). All filesystem entries, including mounted filesystems are "branches" of this root.

Under DOS, OS/2, and Microsoft Windows, each partition has a drive letter assignment (labeled C:\ for a particular partition C) and there is no common root directory above that. DOS, OS/2, and Windows do support more abstract hierarchies, with partitions mountable within a directory of another drive, though this is rarely seen. This has been possible in DOS through the command JOIN since it first was added to DOS, and can be achieved in all Windows versions as well. In some contexts, it is also possible to refer to a root directory containing all mounted drives, although it cannot contain files directly as it does not exist on any file system. For instance, when linking to a local file using the "file:" URI scheme, the syntax is of the form "file:///C:/...", where "file://" is the standard prefix, and the third '/' represents the root of the local system.

In UNIX-like operating systems, each process has its own idea of what the root directory is. For most processes this is the same as the system's actual root directory, but it can be changed by calling the chroot system call. This is typically done for security purposes to restrict which files a process may access to just a subset of the file hierarchy.