sync - synchronize data on disk with memory


SYNOPSYS

       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  noth­
       ing 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 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 imple­
       mentations  of these commands exist; consult your documen­
       tation; on some systems one should not call reboot(8)  and
       halt(8) directly.)


GNU STANDARD 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 1003.2


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

       tions and additions to aeb@cwi.nl.   Report  bugs  in  the
       program to fileutils-bugs@gnu.ai.mit.edu.


SEE ALSO

       sync(2), halt(8), reboot(8), update(8)


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