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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  con‐
       figuration  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 CON‐‐
       FIG_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)

COLOPHON
       This page is part of release 5.10 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 https://www.kernel.org/doc/man-pages/.



Linux                                        2015-01-02                                       MEM(4)