SYNC(8) 		   Linux Programmers 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 man
       ner (e.g., before causing a kernel  panic  when	debugging  new	kernel
       code).	In  general,  the  processor  should be halted using the shut
       down(8) or reboot(8) or halt(8) commands, which will attempt to put the
       system in a quiescent state before calling sync(2).  (Various implemen
       tations 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 success
	      fully.

       --     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 only guaranteed 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 3.05 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)