1mem(4)                     Kernel Interfaces Manual                     mem(4)
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NAME

6       mem, kmem, port - system memory, kernel memory and system ports
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DESCRIPTION

9       /dev/mem is a character device file that is an image of the main memory
10       of the computer.  It may be used, for example,  to  examine  (and  even
11       patch) the system.
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13       Byte  addresses  in  /dev/mem  are  interpreted  as physical memory ad‐
14       dresses.  References to nonexistent locations cause errors  to  be  re‐
15       turned.
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17       Examining  and  patching  is  likely to lead to unexpected results when
18       read-only or write-only bits are present.
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20       Since Linux  2.6.26,  and  depending  on  the  architecture,  the  CON‐
21       FIG_STRICT_DEVMEM  kernel  configuration  option limits the areas which
22       can be accessed through this file.  For example: on x86, RAM access  is
23       not allowed but accessing memory-mapped PCI regions is.
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25       It is typically created by:
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27           mknod -m 660 /dev/mem c 1 1
28           chown root:kmem /dev/mem
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30       The file /dev/kmem is the same as /dev/mem, except that the kernel vir‐
31       tual memory rather than  physical  memory  is  accessed.   Since  Linux
32       2.6.26,  this  file is available only if the CONFIG_DEVKMEM kernel con‐
33       figuration option is enabled.
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35       It is typically created by:
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37           mknod -m 640 /dev/kmem c 1 2
38           chown root:kmem /dev/kmem
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40       /dev/port is similar to /dev/mem, but the I/O ports are accessed.
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42       It is typically created by:
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44           mknod -m 660 /dev/port c 1 4
45           chown root:kmem /dev/port
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FILES

48       /dev/mem
49       /dev/kmem
50       /dev/port
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SEE ALSO

53       chown(1), mknod(1), ioperm(2)
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57Linux man-pages 6.05              2022-10-30                            mem(4)
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