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, mod-
       ified 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 mem-
       ory 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 3.25 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)