aio_write — asynchronous write


#include <aio.h>
int aio_write( struct aiocb *aiocbp);
[Note] Note

Link with −lrt.


The aio_write() function queues the I/O request described by the buffer pointed to by aiocbp. This function is the asynchronous analog of write(2). The arguments of the call

write(fd, buf, count)

correspond (in order) to the fields aio_fildes, aio_buf, and aio_nbytes of the structure pointed to by aiocbp. (See aio(7) for a description of the aiocb structure.)

If O_APPEND is not set, the data is written starting at the absolute position aiocbp−>aio_offset, regardless of the file offset. If O_APPEND is set, data is written at the end of the file in the same order as aio_write() calls are made. After the call, the value of the file offset is unspecified.

The "asynchronous" means that this call returns as soon as the request has been enqueued; the write may or may not have completed when the call returns. One tests for completion using aio_error(3). The return status of a completed I/O operation can be obtained aio_return(3). Asynchronous notification of I/O completion can be obtained by setting aiocbp−>aio_sigevent appropriately; see sigevent(7) for details.

If _POSIX_PRIORITIZED_IO is defined, and this file supports it, then the asynchronous operation is submitted at a priority equal to that of the calling process minus aiocbp−>aio_reqprio.

The field aiocbp−>aio_lio_opcode is ignored.

No data is written to a regular file beyond its maximum offset.


On success, 0 is returned. On error, the request is not enqueued, −1 is returned, and errno is set to indicate the error. If an error is detected only later, it will be reported via aio_return(3) (returns status −1) and aio_error(3) (error status—whatever one would have gotten in errno, such as EBADF).



Out of resources.


aio_fildes is not a valid file descriptor open for writing.


The file is a regular file, we want to write at least one byte, but the starting position is at or beyond the maximum offset for this file.


One or more of aio_offset, aio_reqprio, aio_nbytes are invalid.


aio_write() is not implemented.


The aio_write() function is available since glibc 2.1.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
aio_write() Thread safety MT-Safe


POSIX.1-2001, POSIX.1-2008.


It is a good idea to zero out the control block before use. The control block must not be changed while the write operation is in progress. The buffer area being written out must not be accessed during the operation or undefined results may occur. The memory areas involved must remain valid.

Simultaneous I/O operations specifying the same aiocb structure produce undefined results.


aio_cancel(3), aio_error(3), aio_fsync(3), aio_read(3), aio_return(3), aio_suspend(3), lio_listio(3), aio(7)


This page is part of release 5.11 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−pages/.

  Copyright (c) 2003 Andries Brouwer (

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