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Command: fsync | Section: 2 | Source: OpenBSD | File: fsync.2
FSYNC(2) FreeBSD System Calls Manual FSYNC(2)
NAME
fsync, fdatasync - synchronize a file's in-core state with that on disk
SYNOPSIS
#include <unistd.h>
int
fsync(int fd);
int
fdatasync(int fd);
DESCRIPTION
The fsync() function causes all modified data and attributes of fd to be
moved to a permanent storage device. This normally results in all in-
core modified copies of buffers for the associated file to be written to
a disk.
The fdatasync() function is similar to fsync() except that it only
guarantees modified data (and metadata necessary to read that data) is
committed to storage. Other file modifications may be left
unsynchronized.
fsync() and fdatasync() should be used by programs that require a file to
be in a known state, for example, in building a simple transaction
facility.
If fsync() or fdatasync() fail with EIO, the state of the on-disk data
may have been only partially written. To guard against potential
inconsistency, future calls will continue failing until all references to
the file are closed.
RETURN VALUES
The fsync() and fdatasync() functions return the value 0 if successful;
otherwise the value -1 is returned and the global variable errno is set
to indicate the error.
ERRORS
The fsync() and fdatasync() functions fail if:
[EBADF] fd is not a valid descriptor.
[EINVAL] fd does not refer to a file which can be synchronized.
[EIO] An I/O error occurred while reading from or writing to
the file system.
SEE ALSO
sync(2), sync(8)
STANDARDS
The fsync() and fdatasync() functions conform to IEEE Std 1003.1-2008
("POSIX.1").
HISTORY
The fsync() system call first appeared in 4.1cBSD, and the fdatasync()
function has been available since OpenBSD 5.4.
BUGS
The fdatasync() function is currently a wrapper around fsync(), so it
synchronizes more state than necessary.
FreeBSD 14.1-RELEASE-p8 April 18, 2019 FreeBSD 14.1-RELEASE-p8