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Linux 2.6 - man page for sync (linux section 8)

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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 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
       POSIX.2.

NOTES
       On  Linux,  sync is guaranteed only to schedule the dirty blocks for writing; it can actu-
       ally 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
       http://www.kernel.org/doc/man-pages/.

GNU					    1998-11-01					  SYNC(8)
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