Null device

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: (see TOPS-20) or NUL on CP/M and DOS (internally \DEV\NUL), nul on OS/2 and newer Windows systems^[1] (internally \Device\Null on Windows NT), NIL: on Amiga operating systems,^[2] and NL: on OpenVMS.^[3] In Windows Powershell, the equivalent is $null.^[4] It provides no data to any process that reads from it, yielding EOF immediately.^[5] In IBM operating systems DOS/360 and successors^[a] and also in OS/360 and successors^[b] such files would be assigned in JCL to DD DUMMY.

In programmer jargon, especially Unix jargon, it may also be called the bit bucket^[6] or black hole.

/dev/null is described as an empty regular file in Version 4 Unix.^[7]

The Version 5 Unix manual describes a /dev/null device with modern semantics.^[8]

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. For example, tar -c -f /dev/null "example directory" can be used to dry-run the TAR file archiving utility to see if any errors would occur but without writing any file.

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.

Unix shell command cat /dev/null would do nothing, equivalent to true or : command.

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.^[9] The fictitious person name "Dave (or Devin) Null" is sometimes similarly used (e.g., "send complaints to Dave Null").^[10] 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 "Sends other UNIX boxes to /dev/null."^[11]

The null device is also a favorite subject of technical jokes,^[12] such as warning users that the system's /dev/null is already 98% full. The 1995 April Fool's 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.

Dev/Null is also the name of an electronic dance music producer and jungle DJ.^[13]