SYNC(2)                   FreeBSD System Calls Manual                  SYNC(2)

NAME
     sync - schedule file system updates

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     void
     sync(void);

DESCRIPTION
     The sync() system call 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() system
     call is issued frequently by the kernel process syncer(4) (about every 30
     seconds).

     The fsync(2) system call may be used to synchronize individual file
     descriptor attributes.

SEE ALSO
     fsync(2), syncer(4), sync(8)

HISTORY
     The sync() function appeared in Version 3 AT&T UNIX.

BUGS
     The sync() system call may return before the buffers are completely
     flushed.

FreeBSD 13.1-RELEASE-p6        December 1, 2017        FreeBSD 13.1-RELEASE-p6