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MEM(4) Device Drivers Manual (landisk) MEM(4)

mem, kmemmemory files

The special file /dev/mem is an interface to the physical memory of the computer. Byte offsets in this file are interpreted as physical memory addresses. Reading and writing this file is equivalent to reading and writing memory itself. Only offsets within the bounds of /dev/mem are allowed.

Kernel virtual memory is accessed through the interface /dev/kmem in the same manner as /dev/mem. Only kernel virtual addresses that are currently mapped to memory are allowed.

On landisk, physical memory is contiguous. The kernel virtual memory begins at address 0xc0000000.

Even with sufficient file system permissions, these devices can only be opened when the securelevel(7) is insecure or when the kern.allowkmem sysctl(2) variable is set.



The /dev/mem file appeared in Version 1 AT&T UNIX, /dev/kmem appeared in Version 5 AT&T UNIX.

March 22, 2024 OpenBSD-current