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


   /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

   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




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


   This page is part of release 4.09 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


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