February 6, 2018
fdatasync, fsync - synchronise changes to a file
.In unistd.h int
fdatasync int fdint
fsync int fd
fsyncsystem 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.
fdatasyncsystem 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.
fsyncsystem 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
fdatasynccan be more efficient than
fsynccalls are cancellation points.
.Rv -std fsync
fdatasynccalls fail if:
|The fd argument is not a valid descriptor.|
|The fd argument refers to a socket, not to a file.|
||An I/O error occurred while reading from or writing to the file system.|
.Fx 11.1 .
fsyncsystem call appeared in BSD 4.2 . The
fdatasyncsystem call appeared in
.Fx 11.1 .
fdatasyncsystem call currently does not guarantee that enqueued aio(4) requests for the file referenced by fd are completed before the syscall returns.