sync(8) [freebsd man page]

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

NAME

     sync -- force completion of pending disk writes (flush cache)

SYNOPSIS

     sync

DESCRIPTION

     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

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

NAME

       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 file system 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

       POSIX.2.

NOTES

       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 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    1998-11-01								   SYNC(8)