update(8) [v7 man page]

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

NAME

       update - periodically update the super block

SYNOPSIS

       /etc/update

DESCRIPTION

       Update  is  a program that executes the sync(2) primitive every 30 seconds.  This insures that the file system is fairly up to date in case
       of a crash.  This command should not be executed directly, but should be executed out of the initialization shell command file.

SEE ALSO

       sync(2), sync(1), init(8)

BUGS

       With update running, if the CPU is halted just as the sync is executed, a file system can be damaged.  This is partially due to	DEC  hard-
       ware that writes zeros when NPR requests fail.  A fix would be to have sync(1) temporarily increment the system time by at least 30 seconds
       to trigger the execution of update.  This would give 30 seconds grace to halt the CPU.

																	 UPDATE(8)

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 file system 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 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 3.44 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)