iopl — change I/O privilege level
iopl() changes the I/O
privilege level of the calling process, as specified by the
two least significant bits in
This call is necessary to allow 8514-compatible X servers to run under Linux. Since these X servers require access to all 65536 I/O ports, the ioperm(2) call is not sufficient.
In addition to granting unrestricted I/O port access, running at a higher I/O privilege level also allows the process to disable interrupts. This will probably crash the system, and is not recommended.
The I/O privilege level for a normal process is 0.
This call is mostly for the i386 architecture. On many other architectures it does not exist or will always return an error.
On success, zero is returned. On error, −1 is
errno is set
greater than 3.
This call is unimplemented.
The calling process has insufficient privilege to
is required to raise the I/O privilege level above its
iopl() is Linux-specific and
should not be used in programs that are intended to be
Glibc2 has a prototype both in
Avoid the latter, it is available on i386 only.
Prior to Linux 3.7, on some architectures (such as i386),
inherited by the child produced by fork(2) and were preserved
across execve(2). This behavior
was inadvertently changed in Linux 3.7, and won't be
This page is part of release 4.07 of the Linux
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description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright 1993 Rickard E. Faith (faithcs.unc.edu)
Portions extracted from linux/kernel/ioport.c (no copyright notice).
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Modified Tue Aug 1 16:47 1995 by Jochen Karrer
Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esrthyrsus.com>
Modified Fri Nov 27 14:50:36 CET 1998 by Andries Brouwer <aebcwi.nl>
Modified, 27 May 2004, Michael Kerrisk <mtk.manpagesgmail.com>
Added notes on capability requirements