Provided by: manpages-dev_3.23-1_all
iopl - change I/O privilege level
int iopl(int level);
iopl() changes the I/O privilege level of the calling process, as
specified 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 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
Permissions are inherited by fork(2) and 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.
On success, zero is returned. On error, -1 is returned, and errno is
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.
iopl() is Linux-specific and should not be used in processes intended
to be portable.
Libc5 treats it as a system call and has a prototype in <unistd.h>.
Glibc1 does not have a prototype. Glibc2 has a prototype both in
<sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.