MEM(4D) Devices MEM(4D)
NAME
mem, kmem, allkmem - physical or virtual memory access
SYNOPSIS
/dev/mem
/dev/kmem
/dev/allkmem
DESCRIPTION
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).
ERRORS
EFAULT Occurs when trying to
write(2) a read-only location (
allkmem),
read(2) a write-only location (
allkmem), or
read(2) or
write(2) a non-existent or unimplemented location (
mem,
kmem,
allkmem).
EIO Occurs when trying to
read(2) or
write(2) a memory location
that is associated with an I/O device using the
/dev/kmem special file.
ENXIO Results from attempting to
mmap(2) a non-existent physical
(
mem) or virtual (
kmem,
allkmem) memory address.
FILES
/dev/mem Provides access to the computer's physical memory.
/dev/kmem Provides access to the virtual address space of the
operating system kernel, excluding memory that is
associated with an I/O device.
/dev/allkmem Provides access to the virtual address space of the
operating system kernel, including memory that is
associated with an I/O device.
SEE ALSO
llseek(2),
mmap(2),
read(2),
write(2)WARNINGS
Using these devices to modify (that is, write to) the address space of a
live running operating system or to modify the state of a hardware
device is extremely dangerous and may result in a system panic if kernel
data structures are damaged or if device state is changed.
February 18, 2002
MEM(4D)