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sync(8) [freebsd man page]

SYNC(8) 						    BSD System Manager's Manual 						   SYNC(8)

sync -- force completion of pending disk writes (flush cache) SYNOPSIS
The sync utility can be called to ensure that all disk writes have been completed before the processor is halted in a way not suitably done by reboot(8) or halt(8). Generally, it is preferable to use reboot(8) or halt(8) to shut down the system, as they may perform additional actions such as resynchronizing the hardware clock and flushing internal caches before performing a final sync. The sync utility utilizes the sync(2) function call. SEE ALSO
fsync(2), sync(2), syncer(4), halt(8), reboot(8) HISTORY
A sync utility appeared in Version 4 AT&T UNIX. BSD
May 31, 1993 BSD

Check Out this Related Man Page

SYNC(8) 						     Linux Programmer's Manual							   SYNC(8)

sync - synchronize data on disk with memory SYNOPSIS
sync [--help] [--version] DESCRIPTION
sync writes any data buffered in memory out to disk. This can include (but is not limited to) modified superblocks, modified inodes, and delayed reads and writes. This must be implemented by the kernel; The sync program does nothing but exercise the sync(2) system call. The kernel keeps data in memory to avoid doing (relatively slow) disk reads and writes. This improves performance, but if the computer crashes, data may be lost or the filesystem corrupted as a result. sync ensures that everything in memory is written to disk. sync should be called before the processor is halted in an unusual manner (e.g., before causing a kernel panic when debugging new kernel code). In general, the processor should be halted using the shutdown(8) or reboot(8) or halt(8) commands, which will attempt to put the system in a quiescent state before calling sync(2). (Various implementations of these commands exist; consult your documentation; on some systems one should not call reboot(8) and halt(8) directly.) OPTIONS
--help Print a usage message on standard output and exit successfully. --version Print version information on standard output, then exit successfully. -- Terminate option list. ENVIRONMENT
The variables LANG, LC_ALL, LC_CTYPE, and LC_MESSAGES have the usual meaning. CONFORMING TO
On Linux, sync is guaranteed only to schedule the dirty blocks for writing; it can actually take a short time before all the blocks are finally written. The reboot(8) and halt(8) commands take this into account by sleeping for a few seconds after calling sync(2). This page describes sync as found in the fileutils-4.0 package; other versions may differ slightly. SEE ALSO
sync(2), halt(8), reboot(8), update(8) COLOPHON
This page is part of release 3.55 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at GNU
1998-11-01 SYNC(8)
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