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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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iopl(2) System Calls Manual iopl(2)
iopl - change I/O privilege level
Standard C library (libc, -lc)
#include <sys/io.h>
[[deprecated]] int iopl(int level);
iopl() changes the I/O privilege level of the calling thread, as
specified by the two least significant bits in level.
The I/O privilege level for a normal thread is 0. Permissions are
inherited from parents to children.
This call is deprecated, is significantly slower than ioperm(2),
and is only provided for older X servers which require access to
all 65536 I/O ports. It 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 returned, and errno
is set to indicate the error.
EINVAL level is greater than 3.
ENOSYS This call is unimplemented.
EPERM The calling thread has insufficient privilege to call
iopl(); the CAP_SYS_RAWIO capability is required to raise
the I/O privilege level above its current value.
glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>.
Avoid the latter, it is available on i386 only.
Linux.
Prior to Linux 5.5 iopl() allowed the thread to disable interrupts
while running at a higher I/O privilege level. This will probably
crash the system, and is not recommended.
Prior to Linux 3.7, on some architectures (such as i386),
permissions were 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 reinstated.
ioperm(2), outb(2), capabilities(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 iopl(2)
Pages that refer to this page: ioperm(2), outb(2), syscalls(2), unimplemented(2), systemd.exec(5), capabilities(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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