mem(4) – alpha memory files
mem(4) – amd64 memory files
mem(4) – hppa memory files and memory controller
mem(4) – i386 memory files
mem(4) – landisk memory files
mem(4) – loongson memory files
mem(4) – luna88k memory files
mem(4) – macppc memory files
mem(4) – sparc64 memory files
MEM(4) Device Drivers Manual (sparc64) MEM(4)

mem, kmem — memory files

The 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. An error will be returned if an attempt is made to reference an offset outside of /dev/mem.

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

On the sparc64, physical memory may be discontiguous; kernel virtual memory begins at 0x001000000.

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.

/dev/mem
 
/dev/kmem
 

securelevel(7)

The /dev/mem and /dev/kmem files appeared in Version 6 AT&T UNIX.

January 12, 2018 OpenBSD 7.5