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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 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

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

Linux                                                                          2015-01-02                                                                         MEM(4)