1. History

2. Usage

3. References in computer culture

4. See also

5. References

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\ull 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 Berkeley 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 readfile's.

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.^[5] The fictitious person name "Dave (or Devin) Null" is sometimes similarly used (e.g., "send complaints to Dave Null").^[6] 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 The Masquerade – Redemption. A 2002 advertisement for the Titanium PowerBook G4 reads The Titanium Powerbook G4 Sends other UNIX boxes to /dev/null.^[7]

The null device is also a favorite subject of technical jokes,^[8] 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

• Filesystem Hierarchy Standard
• Memory hole
• rm (Unix)
• Standard streams
• Unix philosophy
• Write-only memory

References

• Nobottle
• No Boundaries (Eva Cassidy album)
• Nobr
• No Brand Con
• No-break space
• No-Break Space
• Nobre Governador Carvalho Bridge
• Nobska Light
• Nobuaki Iwatake
• No-Budget Cinema
• No-budget cinema
• No-budget filmmakers
• No-budget filmmaking
• Nobuhide Oda
• Nobuhiro Kawasato
• Nobuhiro Watsuki
• Nobuhisa Kojima
• Nobuhito, Prince Takamatsu
• Nobukatsu Fujioka
• Nobukazu Takemura
• Nobuko
• Nobuko Aso
• Nobuko Miyamoto
• Nobumori Sugimori
• Nobumoto Mizuno