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.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\" Modified Tue Aug  1 16:47    1995 by Jochen Karrer
.\"                              <cip307@cip.physik.uni-wuerzburg.de>
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.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\"     Added notes on capability requirements
.\"
.TH IOPL 2 2004-05-27 "Linux" "Linux Programmer's Manual"
.SH NAME
iopl \- change I/O privilege level
.SH SYNOPSIS
.B #include <sys/io.h>
.sp
.BI "int iopl(int " level );
.SH DESCRIPTION
.BR iopl ()
changes the I/O privilege level of the current process, as specified in
.IR level .

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
.BR 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.

Permissions are inherited by
.BR fork (2)
and
.BR execve (2).

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.
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
.I level
is greater than 3.
.TP
.B ENOSYS
This call is unimplemented.
.TP
.B EPERM
The calling process has insufficient privilege to call
.BR iopl ();
the
.B CAP_SYS_RAWIO
capability is required.
.SH "CONFORMING TO"
.BR iopl ()
is Linux specific and should not be used in processes
intended to be portable.
.SH NOTES
Libc5 treats it as a system call and has a prototype in
.IR <unistd.h> .
Glibc1 does not have a prototype.
Glibc2 has a prototype both in
.I <sys/io.h>
and in
.IR <sys/perm.h> .
Avoid the latter, it is available on i386 only.
.SH "SEE ALSO"
.BR ioperm (2),
.BR capabilities (7)