Section: POSIX Programmer's Manual (3P)
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.
--- file space control
int posix_fallocate(int fd, off_t offset, off_t len);
function shall ensure that any required storage for regular file data
and continuing for
bytes is allocated on the file system storage media. If
returns successfully, subsequent writes to the specified file data
shall not fail due to the lack of free space on the file system storage
is beyond the current file size, then
shall adjust the file size to
Otherwise, the file size shall not be changed.
It is implementation-defined whether a previous
call influences allocation strategy.
Space allocated via
shall be freed by a successful call to
that truncates the size of the file. Space allocated via
may be freed by a successful call to
that reduces the file size to a size smaller than
Upon successful completion,
shall return zero; otherwise, an error number shall be returned to
indicate the error.
function shall fail if:
argument is not a valid file descriptor.
argument references a file that was opened without write permission.
The value of
is greater than the maximum file size.
A signal was caught during execution.
argument is less than zero, or the
argument is less than zero, or the underlying file system does not
support this operation.
An I/O error occurred while reading from or writing to a file system.
argument does not refer to a regular file.
There is insufficient free space remaining on the file system storage
argument is associated with a pipe or FIFO.
function may fail if:
argument is zero.
The following sections are informative.
function is part of the Advisory Information option and need not be
provided on all implementations.
The Base Definitions volume of POSIX.1-2017,
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
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