null(4) [linux man page]

NULL(4) 						     Linux Programmer's Manual							   NULL(4)

NAME

       null, zero - data sink

DESCRIPTION

       Data written to a null or zero special file is discarded.

       Reads  from the null special file always return end of file (i.e., read(2) returns 0), whereas reads from zero always return bytes contain-
       ing zero ( characters).

       null and zero are typically created by:

	      mknod -m 666 /dev/null c 1 3
	      mknod -m 666 /dev/zero c 1 5
	      chown root:root /dev/null /dev/zero

FILES

       /dev/null
       /dev/zero

NOTES

       If these devices are not writable and readable for all users, many programs will act strangely.

SEE ALSO

       chown(1), mknod(1), full(4)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2009-02-23								   NULL(4)

MEM(4)							     Linux Programmer's Manual							    MEM(4)

NAME

       mem, kmem, port - system memory, kernel memory and system ports

DESCRIPTION

       mem  is	a  character  device  file that is an image of the main memory of the computer.  It may be used, for example, to examine (and even
       patch) the system.

       Byte addresses in mem are interpreted as physical memory addresses.  References to nonexistent locations cause errors to be returned.

       Examining and patching is likely to lead to unexpected results when read-only or write-only bits are present.

       It is typically created by:

	      mknod -m 660 /dev/mem c 1 1
	      chown root:kmem /dev/mem

       The file kmem is the same as mem, except that the kernel virtual memory rather than physical memory is accessed.

       It is typically created by:

	      mknod -m 640 /dev/kmem c 1 2
	      chown root:kmem /dev/kmem

       port is similar to mem, but the I/O ports are accessed.

       It is typically created by:

	      mknod -m 660 /dev/port c 1 4
	      chown root:mem /dev/port

FILES

       /dev/mem
       /dev/kmem
       /dev/port

SEE ALSO

       chown(1), mknod(1), ioperm(2)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    1992-11-21								    MEM(4)