POSIX_FALLOCATE(3P) POSIX Programmer's Manual POSIX_FALLOCATE(3P)PROLOG
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.
NAMEposix_fallocate — file space control (ADVANCED REALTIME)
int posix_fallocate(int fd, off_t offset, off_t len);
The posix_fallocate() function shall ensure that any required storage
for regular file data starting at offset and continuing for len bytes
is allocated on the file system storage media. If posix_fallocate()
returns successfully, subsequent writes to the specified file data
shall not fail due to the lack of free space on the file system storage
If the offset+len is beyond the current file size, then posix_fallo‐
cate() shall adjust the file size to offset+len. Otherwise, the file
size shall not be changed.
It is implementation-defined whether a previous posix_fadvise() call
influences allocation strategy.
Space allocated via posix_fallocate() shall be freed by a successful
call to creat() or open() that truncates the size of the file. Space
allocated via posix_fallocate() may be freed by a successful call to
ftruncate() that reduces the file size to a size smaller than off‐
Upon successful completion, posix_fallocate() shall return zero; other‐
wise, an error number shall be returned to indicate the error.
The posix_fallocate() function shall fail if:
EBADF The fd argument is not a valid file descriptor.
EBADF The fd argument references a file that was opened without write
EFBIG The value of offset+len is greater than the maximum file size.
EINTR A signal was caught during execution.
EINVAL The len argument is less than zero, or the offset argument is
less than zero, or the underlying file system does not support
EIO An I/O error occurred while reading from or writing to a file
ENODEV The fd argument does not refer to a regular file.
ENOSPC There is insufficient free space remaining on the file system
ESPIPE The fd argument is associated with a pipe or FIFO.
The posix_fallocate() function may fail if:
EINVAL The len argument is zero.
The following sections are informative.
The posix_fallocate() function is part of the Advisory Information
option and need not be provided on all implementations.
SEE ALSOcreat(), ftruncate(), open(), unlink()
The Base Definitions volume of POSIX.1‐2008, <fcntl.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
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