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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  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 3.27 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/.