MEM(4)                    (2015-01-02)                     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 mem-
          ory 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

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     MEM(4)                    (2015-01-02)                     MEM(4)

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

     COLOPHON
          This page is part of release 5.10 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/.

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