io_setup — create an asynchronous I/O context


#include <linux/aio_abi.h>          /* Defines needed types */

int io_setup(unsigned nr_events, aio_context_t *ctx_idp);

Note: There is no glibc wrapper for this system call; see Notes.


The io_setup() system call creates an asynchronous I/O context suitable for concurrently processing nr_events operations. The ctx_idp argument must not point to an AIO context that already exists, and must be initialized to 0 prior to the call. On successful creation of the AIO context, *ctx_idp is filled in with the resulting handle.

Return Value

On success, io_setup() returns 0. For the failure return, see Notes.



The specified nr_events exceeds the user's limit of available events, as defined in /proc/sys/fs/aio-max-nr.


An invalid pointer is passed for ctx_idp.


ctx_idp is not initialized, or the specified nr_events exceeds internal limits. nr_events should be greater than 0.


Insufficient kernel resources are available.


io_setup() is not implemented on this architecture.


The asynchronous I/O system calls first appeared in Linux 2.5.

Conforming to

io_setup() is Linux-specific and should not be used in programs that are intended to be portable.


Glibc does not provide a wrapper function for this system call. You could invoke it using syscall(2). But instead, you probably want to use the io_setup() wrapper function provided by libaio.

Note that the libaio wrapper function uses a different type (io_context_t *) for the ctx_idp argument. Note also that the libaio wrapper does not follow the usual C library conventions for indicating errors: on error it returns a negated error number (the negative of one of the values listed in Errors). If the system call is invoked via syscall(2), then the return value follows the usual conventions for indicating an error: -1, with errno set to a (positive) value that indicates the error.

See Also

io_cancel(2), io_destroy(2), io_getevents(2), io_submit(2), aio(7)


This page is part of release 5.04 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

Referenced By

aio(7), fork(2), io_cancel(2), io_destroy(2), io_getevents(2), ioping(1), io_submit(2), stress-ng(1), syscalls(2), systemd.exec(5).

2017-09-15 Linux Programmer's Manual