mem(4) — Linux manual page


mem(4)                  Kernel Interfaces Manual                  mem(4)

NAME         top

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

DESCRIPTION         top

       /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

       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         top


SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                           mem(4)