redhat man page for sync

SYNC(8) 						      System Manager's Manual							   SYNC(8)

NAME
       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 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.)

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 package; other versions may differ slightly.  Mail corrections 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)

GNU fileutils 4.0						      1998-11								   SYNC(8)