|FSYNC(2)||System Calls Manual||FSYNC(2)|
synchronize a file's in-core state with that on
causes all modified data and attributes of fildes 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
Note that while
will flush all data from the host to the drive (i.e. the "permanent
storage device"), the drive itself may not physically write the data to
the platters for quite some time and it may be written in an out-of-order
Specifically, if the drive loses power or the OS crashes, the application may find that only some or none of their data was written. The disk drive may also re-order the data so that later writes may be present, while earlier writes are not.
This is not a theoretical edge case. This scenario is easily reproduced with real world workloads and drive power failures.
For applications that require tighter guarantees about the integrity of their data, Mac OS X provides the F_FULLFSYNC fcntl. The F_FULLFSYNC fcntl asks the drive to flush all buffered data to permanent storage. Applications, such as databases, that require a strict ordering of writes should use F_FULLFSYNC to ensure that their data is written in the order they expect. Please see fcntl(2) for more detail.
fsync() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate the
fsync() system call will fail if:
fsync() function call appeared in
|June 4, 1993||BSD 4.2|