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FSYNC(2) System Calls Manual FSYNC(2) NAME fsync -- synchronize a file's in-core state with that on disk SYNOPSIS #include <unistd.h> int fsync(int fd); DESCRIPTION Fsync() causes all modified data and attributes of fd to be moved to a permanent storage device. This normally results in all in-core modi- fied copies of buffers for the associated file to be written to a disk. Note that while fsync() will flush all data from the host to the drive (i.e. the "permanent storage device"), the drive itself may not physi- cally write the data to the platters for quite some time and it may be written in an out-of-order sequence. Specifically, if the drive loses power or the OS crashes, the applica- tion 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 repro- duced with real world workloads and drive power failures. For applications that require tighter guarantess about the integrity of their data, MacOS 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 their data is written in the order they expect. Please see fcntl(2) for more detail. RETURN VALUES A 0 value is returned on success. A -1 value indicates an error. ERRORS The fsync() fails if: [EBADF] fd is not a valid descriptor. [EINVAL] fd 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 sync(2), sync(8), update(8), fcntl(2) HISTORY The fsync() function call appeared in 4.2BSD. 4.2 Berkeley Distribution June 4, 1993 FSYNC(2)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY
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