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

NAME

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

DESCRIPTION

       /dev/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 /dev/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.

       Since Linux 2.6.26, and depending on the architecture, the CONFIG_STRICT_DEVMEM kernel configuration option limits the areas which  can	be
       accessed through this file.  For example: on x86, RAM access is not allowed but accessing memory-mapped PCI regions is.

       It is typically created by:

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

       The  file  /dev/kmem  is  the same as /dev/mem, except that the kernel virtual memory rather than physical memory is accessed.  Since Linux
       2.6.26, this file is available only if the CONFIG_DEVKMEM kernel configuration option is enabled.

       It is typically created by:

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

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

       It is typically created by:

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

FILES

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

SEE ALSO

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

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2015-01-02								    MEM(4)