mem, kmem, allkmem - physical or virtual memory access
/dev/mem
/dev/kmem
/dev/allkmem
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. A 32-bit process using large file interfaces 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).
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).
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.
Results from attempting to mmap(2) a non-existent physical (mem) or virtual (kmem, allkmem) memory address.
Provides access to the computer's physical memory.
Provides access to the virtual address space of the operating system kernel, excluding memory that is associated with an I/O device.
Provides access to the virtual address space of the operating system kernel, including memory that is associated with an I/O device.
llseek(2), mmap(2), read(2), write(2)
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.