Unix file types

The seven standard Unix file types are regular, directory, symbolic link, FIFO special, block special, character special, and socket as defined by POSIX. These types are used in the file system(s) of a Unix or Unix-likeoperating system (OS). Different OS-specific implementations allow more types than what POSIX requires (e.g. doors in Solaris). A file's type can be identified by the ls -l command, which displays the type in the first character of the file-system permissions field.

For regular files, Unix does not impose or provide any internal file structure (this may be called file format); therefore, their structure and interpretation is entirely dependent on the software using them. However, the file command can usually be used to determine what type of data they contain.