mem



MEM(4)                   Device Drivers Manual (amd64)                  MEM(4)


NAME

     mem, kmem - memory files


DESCRIPTION

     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 amd64, physical memory is discontiguous; especially, the ISA I/O
     memory space covers the physical address range from 0x000a0000 to
     0x00100000.

     The kernel virtual memory begins at address 0xffffffff80000000.

     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.


FILES

     /dev/mem
     /dev/kmem


SEE ALSO

     mtrr(4), securelevel(7)


HISTORY

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

OpenBSD 6.4                    January 12, 2018                    OpenBSD 6.4

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