Unix filesystem: Difference between revisions

Revision as of 17:22, 16 February 2019

Revision as of 15:56, 18 February 2019

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[[File:Standard-unix-filesystem-hierarchy.svg|thumb|An overview of a [[Unix]] filesystem layout]]

In [[Unix]] and [[operating system]]s inspired by it, the [[file system]] is considered a central component of the operating system.<ref name=" Ritchie">{{cite journal |last1= Ritchie |first1= D.M. |authorlink1= Dennis Ritchie |last2= Thompson |first2= K. |authorlink2= Ken Thompson |title= The UNIX Time-Sharing System |journal= Bell System Tech. J. |volume= 57 |issue= 6 |pages= 1905–1929 |publisher= AT&T |___location= USA |date= July 1978 |archiveurl= https://archive.org/details/bstj57-6-1905 |archivedate= 19 January 2013 |url= http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6770404 |doi=10.1002/j.1538-7305.1978.tb02136.x|citeseerx= 10.1.1.112.595 }}</ref> It was also one of the first parts of the system to be designed and implemented by [[Ken Thompson]] in the first experimental version of Unix, [[History of Unix|dated 1969]].<ref name="evolution"/>

As in other operating systems, the filesystem provides information storage and retrieval, and one of several forms of [[interprocess communication]], in that the many small programs that traditionally form a Unix system can store information in files so that other programs can read them, although [[Pipeline (Unix)|pipes]] complemented it in this role starting with the [[Research Unix|Third Edition]]. Also, the filesystem provides access to other resources through so-called ''[[device file]]s'' that are entry points to [[computer terminal|terminals]], [[computer printer|printers]], and [[computer mouse|mice]].

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{{Main |Unix file types}}

The original Unix file system supported three types of files: ordinary files, [[Directory (computing)|directories]], and "special files", also termed device files.<ref name="Ritchie"/> The [[Berkeley Software Distribution]] (BSD) and [[UNIX System V|System V]] each added a file type to be used for [[interprocess communication]]: BSD added [[Berkeley sockets|sockets]],<ref name="43bsd">{{cite book |last1= Leffler|first1= Samuel J. |authorlink1= Samuel J Leffler |last2= McKusick |first2= Marshall Kirk|authorlink2= Marshall Kirk McKusick |last3= Karels |first3= Michael J. |authorlink3=Michael J. Karels |last4=Quarterman |first4= John S. |authorlink4= John Quarterman |title= The Design and Implementation of the [[Berkeley Software Distribution|4.3BSD UNIX]] Operating System|date=October 1989| publisher= [[Addison-Wesley]]|isbn= 978-0-201-06196-13|title-link= Berkeley Software Distribution }}</ref> while System V added [[Named pipe#In Unix|FIFO files]].

BSD also added [[symbolic link]]s (often termed "symlinks") to the range of file types, which are files that refer to other files, and complement hard links.<ref name="43bsd"/> Symlinks were modeled after a similar feature in [[Multics]],<ref name="FFS">{{cite web|last1=McKusick|display-authors=etal|first1=Marshall Kirk|title=A Fast Filesystem for Unix|url=https://docs.freebsd.org/44doc/smm/05.fastfs/paper.pdf|website=Freebsd.org|publisher=CSRG, UC Berkeley|accessdate=16 November 2016}}</ref> and differ from hard links in that they may span filesystems and that their existence is independent of the target object. Other Unix systems may support additional types of files.<ref>{{man|2|stat|Linux}}</ref>

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:<code>/etc</code>

|Contains system-wide configuration files and system databases; the name stands for ''[[et cetera]]''.<ref name="upe">{{cite book |first1=Brian W. |last1=Kernighan |authorlink1=Brian Kernighan |first2=Rob |last2=Pike |authorlink2=Rob Pike |title=[[The UNIX Programming Environment]] |publisher=Prentice-Hall |year=1984 |pages=63–65|title-link=The UNIX Programming Environment }}</ref> Originally also contained "dangerous maintenance utilities" such as <code>init</code>,<ref name="v7"/> but these have typically been moved to <code>/sbin</code> or elsewhere. Needs to be on the root filesystem itself.

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