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 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 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