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 ad-
       dresses.  References to nonexistent locations cause errors  to  be  re-

       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)

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Linux                             2015-01-02                            MEM(4)
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