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 user process update(8) (about every 30 seconds).
The function fsync(2) may be used to synchronize individual file descrip-
fsync(2), sync(8), update(8)
Sync() may return before the buffers are completely flushed.
A sync() function call appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution