Null device

Special device files

In some operating systems, the null device is a device file that discards all data written to it but reports that the write operation succeeded. This device is called /dev/null on Unix and Unix-like systems, NUL: or NUL on DOS and CP/M, nul on newer Windows systems (internally \Device\Null on Windows NT), NIL: on Amiga operating systems, and the NL: on OpenVMS. In Windows Powershell, the equivalent is $null. It provides no data to any process that reads from it, yielding EOF immediately.[1] In IBM DOS/360, OS/360 (MFT, MVT), OS/390 and z/OS operating systems, such files would be assigned in JCL to DD DUMMY.

In programmer jargon, especially Unix jargon, it may also be called the bit bucket[2] or black hole.

History

According to the Berkley UNIX man page, Version 7 Unix included a null device.[3] AT&T released Version 7 Unix in 1979.[4]

Usage

The null device is typically used for disposing of unwanted output streams of a process, or as a convenient empty file for input streams. This is usually done by redirection.

The /dev/null device is a special file, not a directory, so one cannot move a whole file or directory into it with the Unix mv command. The rm command is the proper way to delete files in Unix.

References in computer culture

This entity is a common inspiration for technical jargon expressions and metaphors by Unix programmers, e.g. "please send complaints to /dev/null", "my mail got archived in /dev/null", and "redirect to /dev/null"—being jocular ways of saying, respectively: "don't bother sending complaints", "my mail was deleted", and "go away". The iPhone Dev Team commonly uses the phrase "send donations to /dev/null", meaning they do not accept donations. The fictitious person name "Dave (or Devin) Null" is sometimes similarly used (e.g., "send complaints to Dave Null").[5] In 1996, Dev Null was an animated virtual reality character created by Leo Laporte for MSNBC's computer and technology TV series The Site. Dev/null is also the name of a vampire hacker in the computer game Vampire: The Masquerade – Redemption. A 2002 advertisement for the Titanium PowerBook G4 reads The Titanium Powerbook G4 Sends other UNIX boxes to /dev/null.[6]

The null device is also a favorite subject of technical jokes,[7] such as warning users that the system's /dev/null is already 98% full. The April Fool's, 1995 issue of the German magazine c't reported on an enhanced /dev/null chip that would efficiently dispose of the incoming data by converting it to a flicker on an internal glowing LED.

See also

References

  1. ↑ "Single Unix Specification Section 10.1: Directory Structure and Files". The Open Group. Retrieved 2012-11-29.
  2. ↑ "bit bucket". Jargon File. Retrieved 2013-12-27.
  3. ↑ "null(4)". The FreeBSD Project. Retrieved 2018-08-18.
  4. ↑ Fiedler, David (October 1983). "The Unix Tutorial / Part 3: Unix in the Microcomputer Marketplace". Byte (magazine). v. 8 (#10 - UNIX): 132–156. ISSN 0360-5280. OCLC 854802500. Retrieved 2018-09-11.
  5. ↑ Goodman, Danny (2004). Spam wars : our last best chance to defeat spammers, scammers, and hackers. New York: SelectBooks. p. 170. ISBN 9781590790632. OCLC 1036874851.
  6. ↑ "Image: unixad.jpg, (1094 × 720 px)". web.archive.org. Archived from the original on March 26, 2013. Retrieved 2015-09-02.
  7. ↑ "The FreeBSD Funnies". Freebsd.org. Retrieved 2012-11-28.
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