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The file /dev/mem is a special file that provides access to the physical memory of
the computer.
The file /dev/kmem is a special file that provides
access to the virtual address space of the operating system kernel, excluding
memory that is associated with an I/O device.
The file /dev/allkmem is a special file that provides
access to the virtual address space of the operating system kernel, including
memory that is associated with an I/O device. You can use any of these devices
to examine and modify the system.
Byte addresses in /dev/mem are interpreted as physical
memory addresses. Byte addresses in /dev/kmem and /dev/allkmem are interpreted as kernel virtual memory addresses.
A reference to a non-existent location returns an error. See ERRORS for more
information.
The file /dev/mem accesses physical memory; the
size of the file is equal to the amount of physical memory in the computer.
This size may be larger than 4GB on a system running the 32-bit operating
environment. In this case, you can access memory beyond 4GB using a series
of read(2) and write(2) calls, a pread64() or pwrite64() call, or a combination
of llseek(2) and read(2) or write(2).
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