iopl(2)			       System Calls Manual			 iopl(2)

NAME
     iopl - change I/O privilege level

LIBRARY
     Standard C library (libc, -lc)

SYNOPSIS
     #include <sys/io.h>

     [[deprecated]] int iopl(int level);

DESCRIPTION
     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  inher-
     ited 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 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
     to indicate the error.

ERRORS
     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.

VERSIONS
     glibc2  has  a prototype both in <sys/io.h> and in <sys/perm.h>.  Avoid the
     latter, it is available on i386 only.

STANDARDS
     Linux.

HISTORY
     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 sys-
     tem, 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  ex-
     ecve(2).	This  behavior was inadvertently changed in Linux 3.7, and won't
     be reinstated.

SEE ALSO
     ioperm(2), outb(2), capabilities(7)

Linux man-pages 6.18		   2026-02-08				 iopl(2)