SYNC(2) BSD System Calls Manual SYNC(2)
sync -- synchronize disk block in-core status with that on disk
The sync() function forces a write of dirty (modified) buffers in the
block buffer cache out to disk. The kernel keeps this information in
core to reduce the number of disk I/O transfers required by the system.
As information in the cache is lost after a system crash a sync() call is
issued frequently by the in-kernel process update (about every 30 sec-
The function fsync(2) may be used to synchronize individual file descrip-
The sync() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').
A sync() function call appeared in Version 2 AT&T UNIX.
sync() may return before the buffers are completely flushed.
BSD August 14, 2013 BSD