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



NAME
       mem, kmem, port - system memory, kernel memory and system ports

DESCRIPTION
       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 mem are interpreted as physical memory addresses.  References to  nonex‐
       istent 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.

       It is typically created by:

              mknod -m 660 /dev/mem c 1 1
              chown root:kmem /dev/mem

       The file kmem is the same as mem, except that the kernel virtual memory rather than physi‐
       cal memory is accessed.

       It is typically created by:

              mknod -m 640 /dev/kmem c 1 2
              chown root:kmem /dev/kmem

       port is similar to mem, but the I/O ports are accessed.

       It is typically created by:

              mknod -m 660 /dev/port c 1 4
              chown root:mem /dev/port

FILES
       /dev/mem
       /dev/kmem
       /dev/port

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

COLOPHON
       This  page  is  part of release 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       1992-11-21                                     MEM(4)