bsd man page for update

UPDATE(8)						      System Manager'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 partially due to	DEC  hard-
       ware 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.

7th Edition							 November 17, 1996							 UPDATE(8)