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


     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  CON-
     FIG_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 vir-
     tual memory rather than  physical  memory  is  accessed.   Since  Linux
     2.6.26,  this  file is available only if the CONFIG_DEVKMEM kernel con-
     figuration 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 4.16 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

Linux 2015-01-02 MEM(4)

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