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mem(4d)

Device Drivers & /dev files                                            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 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 loca‐
       tion 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).

ERRORS
       EFAULT    Occurs when trying to write(2) a  read-only  location  (allk‐
                 mem),  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 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 hardware
       device is extremely dangerous and may result in a system panic if  ker‐
       nel data structures are damaged or if device state is changed.



Oracle Solaris 11.4               11 Dec 2020                          mem(4D)
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