Unix file types

The Unix file types are the categories of file formats that a Unix-based system uses to provide context-sensitive behavior of file system items – all of which called files in Unix-based systems. POSIX defines categories: regular, directory, symbolic link, FIFO special, block special, character special, and socket.^[1] An operating system may define additional categories (e.g. Solaris doors).

A regular file is any file format that the file system does not know and relies on applications to manipulate.^[2] The other categories are for file formats that the file system inherently knows and can manipulate.

The ls -l command reports a file's category via the character before the permissions information. The file command reports file format information; even for regular files.^[3]

^ "<sys/stat.h>". The Open Group Base Specifications Issue 8. The Open Group. 14 June 2024. Archived from the original on 25 April 2025. Retrieved 1 June 2025.
^ Loukides, Mike (October 2002). "When Is a File Not a File?". Unix Power Tools (3 ed.). O'Reilly. p. 80. ISBN 9780596003302. A file is nothing more than a stream of bytes ...
^ "file". IEEE Std 1003.1-2017 (POSIX). The Open Group. 2018. Archived from the original on 2018-10-12. Retrieved 2023-10-26.

[stath-1] "<sys/stat.h>". The Open Group Base Specifications Issue 8. The Open Group. 14 June 2024. Archived from the original on 25 April 2025. Retrieved 1 June 2025.

[2] Loukides, Mike (October 2002). "When Is a File Not a File?". Unix Power Tools (3 ed.). O'Reilly. p. 80. ISBN 9780596003302. A file is nothing more than a stream of bytes ...

[3] "file". IEEE Std 1003.1-2017 (POSIX). The Open Group. 2018. Archived from the original on 2018-10-12. Retrieved 2023-10-26.

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