sync - synchronize disk block in-core status with that on disk
Standard C Library (libc, -lc)
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, kernel thread
ioflush ensures that dirty buffers are synced to disk eventually. By
default, a dirty buffer is synced after 30 seconds, but some filesystems
exploit ioflush features to sync directory data and metadata faster
(after 15 and 10 seconds, respectively).
The function fsync(2) may be used to synchronize individual file descriptor
A sync() function call appeared in Version 6 AT&T UNIX.
sync() may return before the buffers are completely flushed.
BSD June 4, 1993 BSD
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