.\"	$OpenBSD: mem.4,v 1.5 2024/03/22 12:29:33 jsg Exp $
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.\"	from: @(#)mem.4	5.3 (Berkeley) 5/2/91
.\"
.Dd $Mdocdate: March 22 2024 $
.Dt MEM 4 landisk
.Os
.Sh NAME
.Nm mem ,
.Nm kmem
.Nd memory files
.Sh DESCRIPTION
The special file
.Pa /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
.Pa /dev/mem
are allowed.
.Pp
Kernel virtual memory is accessed through the interface
.Pa /dev/kmem
in the same manner as
.Pa /dev/mem .
Only kernel virtual addresses that are currently mapped to memory are allowed.
.Pp
On landisk, physical memory is contiguous.
The kernel virtual memory begins at address
.Li 0xc0000000 .
.Pp
Even with sufficient file system permissions,
these devices can only be opened when the
.Xr securelevel 7
is insecure or when the
.Va kern.allowkmem
.Xr sysctl 2
variable is set.
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /dev/mem
.It Pa /dev/kmem
.El
.Sh SEE ALSO
.Xr securelevel 7
.Sh HISTORY
The
.Pa /dev/mem
file appeared in
.At v1 ,
.Pa /dev/kmem
appeared in
.At v5 .