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sync(2) [netbsd man page]

SYNC(2) 						      BSD System Calls Manual							   SYNC(2)

sync -- synchronize disk block in-core status with that on disk LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> void sync(void); DESCRIPTION
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 attributes. CAUTIONS
Many modern disks contain write-back caches. In theory sync() flushes these. In practice there are many possible ways for this mechanism to go astray. It is prudent (where possible) to allow a few seconds after syncing for everything to settle before e.g. turning off the power. It may also be desirable to use dkctl(8) or scsictl(8) to disable the write-back cache entirely. SEE ALSO
fsync(2), dkctl(8), scsictl(8), sync(8) HISTORY
A sync() function call appeared in Version 6 AT&T UNIX. Historically, sync() would schedule buffers for writing but not actually wait for the writes to finish. It was necessary to issue a second or sometimes a third call to ensure that all buffers had in fact been written out. In NetBSD, sync() does not return until all buffers have been written. BSD
March 25, 2009 BSD

Check Out this Related Man Page

sync(2) 							   System Calls 							   sync(2)

sync - update super block SYNOPSIS
#include <unistd.h> void sync(void); DESCRIPTION
The sync() function writes all information in memory that should be on disk, including modified super blocks, modified inodes, and delayed block I/O. Unlike fsync(3C), which completes the writing before it returns, sync() schedules but does not necessarily complete the writing before returning. USAGE
The sync() function should be used by applications that examine a file system, such as fsck(1M), and df(1M), and is mandatory before rebooting. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
df(1M), fsck(1M), fsync(3C), attributes(5), standards(5) SunOS 5.10 5 Jul 1990 sync(2)
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