/dev/zero

Template:Short description Template:Use dmy dates /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.

Function

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. However, /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.

History

/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.

Examples

Erasing a file system partition or drive:

cp /dev/zero /dev/<destination drive or partition>

However, this may not perform a secure erasure, may not destroy the data at all, and may take significantly more time than required–for this purpose.

Creating a file, called foobar, filled with null characters:

See also

• Unix philosophy
• Standard streams
• /dev
• /dev/null
• /dev/full