/dev/null

In Unix-like operating systems, /dev/null or the null device is a special file that discards all data written to it (but reports that the write operation succeeded) and provides no data to any process that reads from it (yielding EOF immediately).^[1]

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

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.

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

This concept is roughly equivalent to the NUL: or just NUL device of CP/M, DOS and Windows, the \Device\Null or NUL of Windows NT and its successors, the NIL: of Amiga operating systems, and the NL: of OpenVMS. In Windows Powershell, the equivalent is $null.

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".^[3] 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").^{[citation needed]}

The null device is also a favorite subject of technical jokes, 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

• Device file
• Filesystem Hierarchy Standard
• Memory hole
• rm (Unix)
• Standard streams
• /dev/zero
• /dev/random
• /dev/full
• /dev
• Unix philosophy
• Write-only memory

References

1. ^ Single Unix Specification Section 10.1
2. ^ Jargon file entry for "bit bucket"
3. ^ The Linux Kernel Archives FAQ at kernel.org