mem(7D)				    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 physi‐
       cal memory of the computer.

       The file /dev/kmem is a special file that provides access to  the  vir‐
       tual  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  environ‐
       ment.  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).

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 phys‐
		       ical (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 asso‐
		       ciated with an I/O device.

       /dev/allkmem    Provides	 access	 to  the  virtual address space of the
		       operating system kernel, including memory that is asso‐
		       ciated 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	 hard‐
       ware  device is extremely dangerous and may result in a system panic if
       kernel data structures are damaged or if device state is changed.

SunOS 5.10			  18 Feb 2002			       mem(7D)

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