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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 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 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 kmem is the same as mem, except that the kernel virtual memory rather than physical memory is accessed. Since 2.6.26, this file is only available 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

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: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 3.78 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/.

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