Synchronizing a File

fsync(3C) and fdatasync(3RT) explicitly synchronize a file to secondary storage.

The fsync(3C) routine guarantees that the interface is synchronized at the I/O file integrity completion level. fdatasync(3RT) guarantees that the interface is synchronized at level of I/O data integrity completion.

Applications can synchronize each I/O operation before the operation completes. Setting the O_DSYNC flag on the file description by using open(2) or fcntl(2) ensures that all I/O writes reach I/O data completion before the operation completes. Setting the O_SYNC flag on the file description ensures that all I/O writes have reached completion before the operation is indicated as completed. Setting the O_RSYNC flag on the file description ensures that all I/O reads read(2) and aio_read(3RT) reach the same level of completion that is requested by the descriptor setting. The descriptor setting can be either O_DSYNC or O_SYNC.