SYNC(2) System Calls Manual SYNC(2)

sync — synchronize disk block in-core status with that on disk

#include <unistd.h>

void
sync(void);

The () 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 descriptor attributes.

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.

June 4, 1993 BSD 4