/dev/zero is aspecial file inUnix-likeoperating systems that provides as manynull characters (ASCII NUL, 0x00) as are read from it.[1] One of the typical uses is to provide a character stream for initializing data storage.[2]
Read operations from/dev/zero return as manynull 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., withmmap, to the virtual address space, it is equivalent to using anonymous memory; i.e. memory not connected to any file.
/dev/zero was introduced in 1988 in SunOS-4.0 to allow a mappable BSS segment for shared libraries using anonymous memory.[3] HP-UX 8.x introduced the MAP_ANONYMOUS flag for mmap(), which maps anonymous memory directly without a need to open/dev/zero.[4] Since the late 1990s, MAP_ANONYMOUS[5] or MAP_ANON are supported by most UNIX versions, removing the original purpose of/dev/zero.[6]
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Erasing aUSB flash drive usingDD:
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.[citation needed]
Creating a1 MiB file, namedfoobar, filled with null characters:
head-c$((1024*1024))/dev/zero>foobar