sync

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 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 3.61 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)