mem(4) Kernel Interfaces 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 ad-
dresses. References to nonexistent locations cause errors to be re-
turned.
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 CON-
FIG_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 vir-
tual memory rather than physical memory is accessed. Since Linux
2.6.26, this file is available only if the CONFIG_DEVKMEM kernel con-
figuration 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)
Linux man-pages 6.7 2023-10-31 mem(4)
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