mem(7)

NAME
     mem, kmem, mmem - core memory

DESCRIPTION
     The file /dev/mem is a special file that is an image of the core memory
     of the computer.  It may be used, for example, to examine, and even to
     patch the system.

     Byte addresses in /dev/mem are interpreted as memory addresses.
     References to non-existent locations cause errors to be returned.

     Examining and patching device registers is likely to lead to unexpected
     results when read-only or write-only bits are present.

     The file /dev/kmem is similar to /dev/mem except that kernel virtual
     memory, rather than physical memory, is accessed.  read(2) and write(2)
     access is supported, to kernel virtual space that represents physical
     memory.  mmap(2) access to /dev/kmem is not supported.  This is due to
     mmap creating data consistency problems which could lead to corrupted
     data and kernel panics.

     The file /dev/mmem is similar to /dev/kmem except that only mmap(2)
     access is permitted (both read and write), and only for those addresses
     configured into the system via the file /var/sysgen/master.d/mem and the
     /etc/autoconfig script.

FILES
     /dev/mem
     /dev/kmem
     /dev/mmem

WARNING
     Some of /dev/kmem cannot be read because of write-only addresses or
     unequipped memory addresses.