man4/mem.4

   1 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
   2 .\"     Fri Apr  2 11:32:09 MET DST 1993
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  25 .\" Modified Sat Jul 24 16:59:10 1993 by Rik Faith (faith@cs.unc.edu)
  26 .TH MEM 4 2015-01-02 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 mem, kmem, port \- system memory, kernel memory and system ports
  29 .SH DESCRIPTION
  30 .IR /dev/mem
  31 is a character device file
  32 that is an image of the main memory of the computer.
  33 It may be used, for example, to examine (and even patch) the system.
  34 .PP
  35 Byte addresses in
  36 .IR /dev/mem
  37 are interpreted as physical memory addresses.
  38 References to nonexistent locations cause errors to be returned.
  39 .PP
  40 Examining and patching is likely to lead to unexpected results
  41 when read-only or write-only bits are present.
  42 .PP
  43 Since Linux 2.6.26, and depending on the architecture, the
  44 .B CONFIG_STRICT_DEVMEM
  45 kernel configuration option limits the areas
  46 which can be accessed through this file.
  47 For example: on x86, RAM access is not allowed but accessing
  48 memory-mapped PCI regions is.
  49 .PP
  50 It is typically created by:
  51 .PP
  52 .in +4n
  53 .EX
  54 mknod \-m 660 /dev/mem c 1 1
  55 chown root:kmem /dev/mem
  56 .EE
  57 .in
  58 .PP
  59 The file
  60 .IR /dev/kmem
  61 is the same as
  62 .IR /dev/mem ,
  63 except that the kernel virtual memory
  64 rather than physical memory is accessed.
  65 Since Linux 2.6.26, this file is available only if the
  66 .B CONFIG_DEVKMEM
  67 kernel configuration option is enabled.
  68 .PP
  69 It is typically created by:
  70 .PP
  71 .in +4n
  72 .EX
  73 mknod \-m 640 /dev/kmem c 1 2
  74 chown root:kmem /dev/kmem
  75 .EE
  76 .in
  77 .PP
  78 .IR /dev/port
  79 is similar to
  80 .IR /dev/mem ,
  81 but the I/O ports are accessed.
  82 .PP
  83 It is typically created by:
  84 .PP
  85 .in +4n
  86 .EX
  87 mknod \-m 660 /dev/port c 1 4
  88 chown root:kmem /dev/port
  89 .EE
  90 .in
  91 .SH FILES
  92 .I /dev/mem
  93 .br
  94 .I /dev/kmem
  95 .br
  96 .I /dev/port
  97 .SH SEE ALSO
  98 .BR chown (1),
  99 .BR mknod (1),
 100 .BR ioperm (2)