sync

SYNC(8)			  Linux Programmer’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 shut-
       down(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	 suc-
	      cessfully.

       --     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)