/dev/zero
Special file in Unix-like operating systems
/dev/zero is a special file in Unix-like operating systems that provides as many null characters (ASCII NUL, 0x00) as are read from it. One of the typical uses is to provide a character stream for initializing data storage.
01Function
Read operations from /dev/zero return as many null characters (0x00) as requested in the read operation.
All write operations to /dev/zero succeed with no other effects. /dev/null is more commonly used for this purpose.
When /dev/zero is memory-mapped, e.g., with mmap, to the virtual address space, it is equivalent to using anonymous memory; i.e. memory not connected to any file.
02History
/dev/zero was introduced in 1988 in SunOS-4.0 to allow a mappable BSS segment for shared libraries using anonymous memory. HP-UX 8.x introduced the MAP_ANONYMOUS flag for mmap(), which maps anonymous memory directly without a need to open /dev/zero. Since the late 1990s, MAP_ANONYMOUS or MAP_ANON are supported by most UNIX versions, removing the original purpose of /dev/zero.
03Examples
Erasing a USB flash drive using DD:
dd if=/dev/zero of=/dev/<destination drive>This may not perform a secure erasure and may not destroy any data, but may take significantly more time than required for this purpose.
Creating a 1 MiB file, named foobar, filled with null characters:
head -c $((1024 * 1024)) /dev/zero >foobarSources and credits
This article is adapted from the Wikipedia article “/dev/zero”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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