Devices                                                   mem(7D)



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 sys-
     tem.


     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 ERORS 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 com-
     puter. 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 combi-
     nation of llseek(2) and read(2) or write(2).

ERORS
     EFAULT    Occurs when trying to  write(2) a read-only  loca-
               tion  (allkmem),  read(2)  a  write-only  location
               (allkmem), or read(2) or write(2)  a  non-existent
               or unimplemented location (mem, kmem, allkmem).





SunOS 5.11          Last change: 18 Feb 2002                    1






Devices                                                   mem(7D)



     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  dev-
                     ice.


     /dev/allkmem    Provides access to the virtual address space
                     of  the  operating  system kernel, including
                     memory that is associated with an  I/O  dev-
                     ice.


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.



















SunOS 5.11          Last change: 18 Feb 2002                    2