NAME
fdatasync, fsync
— synchronise changes to a
file
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
int
fdatasync(int
fd);
int
fsync(int
fd);
DESCRIPTION
Thefsync()
system call causes all modified data and attributes of the file referenced by
the file descriptor 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()
system call causes all modified data of fd to be moved
to a permanent storage device. Unlike fsync(), the
system call does not guarantee that file attributes or metadata necessary to
access the file are committed to the permanent storage.
The
fsync()
system call should be used by programs that require a file to be in a known
state, for example, in building a simple transaction facility. If the file
metadata has already been committed, using
fdatasync() can be more efficient than
fsync().
Both
fdatasync()
and fsync() calls are cancellation points.
RETURN VALUES
The fsync() function returns 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() calls fail if:
- [
EBADF] - The fd argument is not a valid descriptor.
- [
EINVAL] - The fd argument refers to a socket, not to a file.
- [
EIO] - An I/O error occurred while reading from or writing to the file system.
SEE ALSO
HISTORY
The fsync() system call appeared in
4.2BSD. The fdatasync()
system call appeared in FreeBSD 11.1.
BUGS
The fdatasync() system call currently does
not guarantee that enqueued
aio(4) requests for the file referenced by fd
are completed before the syscall returns.