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 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 3.54 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/.