Special device files |
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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 DeviceNull
on Windows NT), NIL:
on Amiga operating systems, and 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.
If the application just opens the existing file and writes to it then as described in other answers you can symlink it to /dev/null, symlink it somewhere else, hardlink it somewhere else (though hardlinks can't be cross filesystem so there isn't a lot of point in this) create a copy of the /dev/null device node there etc. If you use strace to watch what happens when copying a file, you. Strace -s 8 -xx cp /dev/urandom /dev/null. Read(3, 'x61xcaxf8xffx1axd6x83x8b'. Note that this is highly specific to Linux: other Unix kernels may.
History[edit]
According to the Berkeley UNIX man page, Version 4 Unix, which AT&T released in 1973, included a null device.[3][4]
Usage[edit]
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.References in computer culture[edit]
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 Vampire: 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[edit]
References[edit]
- ^'Single Unix Specification Section 10.1: Directory Structure and Files'. The Open Group. Retrieved 2012-11-29.
- ^'bit bucket'. Jargon File. Retrieved 2013-12-27.
- ^'null(4)'. The NetBSD Project.
- ^'sh(1) manual from version 4 Unix'.
- ^'Dev-Team Blog - Donations to /dev/null'. 2015-09-07. Retrieved 2018-11-15.
- ^Goodman, Danny (2004). Spam wars : our last best chance to defeat spammers, scammers, and hackers. New York: SelectBooks. p. 170. ISBN9781590790632. OCLC1036874851.
- ^'Image: unixad.jpg, (1094 × 720 px)'. Archived from the original on March 26, 2013. Retrieved 2015-09-02.
- ^'The FreeBSD Funnies'. Freebsd.org. Retrieved 2012-11-28.
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