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iopl
<html> <head> <title>iopl</title> <META NAME="KEYWORDS" CONTENT="iopl"> </head> <body BGCOLOR="#ffffff" LINK="#0000ff" VLINK="#0000ff" ALINK="#0000ff" TEXT="#000000"> <center> <h1><b>iopl</b></h1></center> <PRE> <STRONG><A HREF="/man2/IOPL">IOPL(2)</A></STRONG> Linux Programmer's Manual <STRONG><A HREF="/man2/IOPL">IOPL(2)</A></STRONG> NAME iopl - change I/O privilege level SYNOPSIS #include <sys/io.h> int iopl(int level); DESCRIPTION iopl() changes the I/O privilege level of the calling process, as spec- ified by the two least significant bits in 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 <STRONG><A HREF="/man2/ioperm">ioperm(2)</A></STRONG> 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 inter- rupts. This will probably crash the system, and is not recommended. Permissions are not inherited by the child process created by <STRONG><A HREF="/man2/fork">fork(2)</A></STRONG> and are not preserved across <STRONG><A HREF="/man2/execve">execve(2)</A></STRONG> (but see NOTES). The I/O privilege level for a normal process is 0. This call is mostly for the i386 architecture. On many other architec- tures it does not exist or will always return an error. RETURN VALUE On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS EINVAL level is greater than 3. ENOSYS This call is unimplemented. EPERM The calling process has insufficient privilege to call iopl(); the CAP_SYS_RAWIO capability is required to raise the I/O privi- lege level above its current value. CONFORMING TO iopl() is Linux-specific and should not be used in programs that are intended to be portable. NOTES Glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only. Prior to Linux 3.7, on some architectures (such as i386), permissions were inherited by the child produced by <STRONG><A HREF="/man2/fork">fork(2)</A></STRONG> and were preserved across <STRONG><A HREF="/man2/execve">execve(2)</A></STRONG>. This behavior was inadvertently changed in Linux 3.7, and won't be reinstated. SEE ALSO <STRONG><A HREF="/man2/ioperm">ioperm(2)</A></STRONG>, <STRONG><A HREF="/man2/outb">outb(2)</A></STRONG>, <STRONG><A HREF="/man7/capabilities">capabilities(7)</A></STRONG> COLOPHON This page is part of release 5.05 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 https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 <STRONG><A HREF="/man2/IOPL">IOPL(2)</A></STRONG></PRE> <center> <h6>Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2025 <a href="http://www.he.net">Hurricane Electric</a>. All Rights Reserved.</h6></center> </body> </html>