--- name: "iopl" section: "2" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/iopl" --- # iopl(2) change I/O privilege level ## NAME iopl - change I/O privilege level ## LIBRARY Standard C library (*libc*, *-lc*) ## SYNOPSIS ``` #include ``` **\[\[deprecated\]\] 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 inherited from parents to children. This call is deprecated, is significantly slower than [**ioperm**(2)](/ioperm/2.md), 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. ## 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 *\* and in *\*. 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 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)](/fork/2.md) and were preserved across [**execve**(2)](/execve/2.md). This behavior was inadvertently changed in Linux 3.7, and won't be reinstated. ## SEE ALSO [**ioperm**(2)](/ioperm/2.md), [**outb**(2)](/outb/2.md), [**capabilities**(7)](/capabilities/7.md)