Comparison

System Call	Target	Content
`sync`	All files that are not sync	data + metadata
`fsync`	Specific file descriptor	data + metadata
`fdatasync`	Specific file descriptor	data

Detail

sync

void sync();

Queue every modified block buffers to the event queue
Will be call by the system on a regular interval (~30s)
Non-blocking

fsync

int fsync(int filedes);

Sync data and metadata of the designated file descriptor
Blocking

fdatasync

int fdatasync(int filedes);

Sync only the data of the designated file descriptor and neglect the metadata
Blocking