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MEM(4) - Linux manual page online | Special files

System memory, kernel memory and system ports.

MEM(4) Linux Programmer's Manual MEM(4)


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


/dev/mem is a character device file that is an image of the main memory of the computer. It may be used, for example, to examine (and even patch) the system. Byte addresses in /dev/mem are interpreted as physical memory addresses. References to nonexistent locations cause errors to be returned. Examining and patching is likely to lead to unexpected results when read-only or write- only bits are present. Since Linux 2.6.26, and depending on the architecture, the CONFIG_STRICT_DEVMEM kernel configuration option limits the areas which can be accessed through this file. For exam‐ ple: on x86, RAM access is not allowed but accessing memory-mapped PCI regions is. It is typically created by: mknod -m 660 /dev/mem c 1 1 chown root:kmem /dev/mem The file /dev/kmem is the same as /dev/mem, except that the kernel virtual memory rather than physical memory is accessed. Since Linux 2.6.26, this file is available only if the CONFIG_DEVKMEM kernel configuration option is enabled. It is typically created by: mknod -m 640 /dev/kmem c 1 2 chown root:kmem /dev/kmem /dev/port is similar to /dev/mem, but the I/O ports are accessed. It is typically created by: mknod -m 660 /dev/port c 1 4 chown root:kmem /dev/port


/dev/mem /dev/kmem /dev/port


chown(1), mknod(1), ioperm(2)


This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at
Linux 2015-01-02 MEM(4)
This manual Reference Other manuals
mem(4) referred by biosdecode(8) | dmidecode(8) | inb(1) | io(4freebsd) | kmem(4freebsd) | mem(4freebsd) | Mojolicious::Controller(3pm) | ownership(8) | pg_top(1) | vpddecode(8) | xisdnload(1x) | xload(1)
refer to chown(1) | ioperm(2) | mknod(1)
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