/ dev / null
/ dev / null is the implementation of the zero device ( English null device ) as a special file in Unix - operating systems . It has its origin /dev/null
in the operating system UNIX Version 7 from 1977, the behavior of the implementation was defined in the POSIX standard.
This is essential for SUS -certified and POSIX-compliant UNIX operating /dev/null
systems. Many other Unix-like operating systems, including BSD- based Unix such as the BSD successor projects NetBSD , FreeBSD and OpenBSD as well as Linux , adhere to the standard specified with POSIX for the null device. On other operating systems, /dev/null
POSIX-compliant Unix shells are also implemented, for example with Cygwin under Windows .
use
If /dev/null
the output is addressed, a data stream to be output is discarded. When read access to ( entry ) is a single end-of-file character ( EOF
issued). The primary use of /dev/null
is to discard expenses.
In addition, the null device can also serve as a pseudo addressee. For example, the command copies
cp Datei /dev/null
(see cp
) the mentioned source file, in the example Datei
, effectively nowhere, but by reading the source file, which is necessary for the process, on the one hand its complete readability is determined ( i.e. serves as a kind of selective fsck ), on the other hand the source file is loaded into the disk cache by reading , which speeds up any subsequent use. Moreover - depends on the file system of the - inode -content changed because the access time stamp ( English time access , short atime ) is reset.
Read accesses only deliver a single end-of-file symbol, which is why it can also be used to generate "empty entries". The following example creates a new, empty file by copying the device file:
cp /dev/null "leere Datei.txt"
Reception in net culture
In net culture , /dev/null
a term used colloquially expresses disinterest in or contempt for an object by suggesting its rejection. An example would be the pseudo command mv program /dev/null
, which amounts to “throw the program away”.
The saying “For backups there is / dev / null, for restores / dev / random …” is also known, which sarcastically comments on the often little or insufficiently tested backup procedures.