2.11BSD#431 - /usr/man/cat8/update.0

UPDATE(8)	    UNIX Programmer's Manual		UPDATE(8)


NAME
     update - periodically update the super block

SYNOPSIS
     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(8), init(8), rc(8)

BUGS
     With update running, if the CPU is halted just as the sync
     is executed, a file system can be damaged.  This is par-
     tially due to DEC hardware that writes zeros when NPR
     requests fail.  A fix would be to have sync(8) 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.


Printed 11/26/99	November 17, 1996			1