This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

posix_fadvise — file advisory information (ADVANCED REALTIME)

#include <fcntl.h>
int posix_fadvise(int fd, off_t offset, off_t len, int advice);

The posix_fadvise() function shall advise the implementation on the expected behavior of the application with respect to the data in the file associated with the open file descriptor, fd, starting at offset and continuing for len bytes. The specified range need not currently exist in the file. If len is zero, all data following offset is specified. The implementation may use this information to optimize handling of the specified data. The posix_fadvise() function shall have no effect on the semantics of other operations on the specified data, although it may affect the performance of other operations.

The advice to be applied to the data is specified by the advice parameter and may be one of the following values:


Specifies that the application has no advice to give on its behavior with respect to the specified data. It is the default characteristic if no advice is given for an open file.

Specifies that the application expects to access the specified data sequentially from lower offsets to higher offsets.

Specifies that the application expects to access the specified data in a random order.

Specifies that the application expects to access the specified data in the near future.

Specifies that the application expects that it will not access the specified data in the near future.

Specifies that the application expects to access the specified data once and then not reuse it thereafter.

These values are defined in <fcntl.h>.

Upon successful completion, posix_fadvise() shall return zero; otherwise, an error number shall be returned to indicate the error.

The posix_fadvise() function shall fail if:
The fd argument is not a valid file descriptor.
The value of advice is invalid, or the value of len is less than zero.
The fd argument is associated with a pipe or FIFO.

The following sections are informative.


The posix_fadvise() function is part of the Advisory Information option and need not be provided on all implementations.




The Base Definitions volume of POSIX.1‐2017, <fcntl.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

2017 IEEE/The Open Group