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       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 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




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


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