mem <root
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 exam‐
       ple: 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 4.04 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 http://www.kernel.org/doc/man-pages/.

Linux                                       2015-01-02                                     MEM(4)

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