4.3BSD - /usr/man/cat8/update.0

UPDATE(8)                                                            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 sec‐
       onds.  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 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.


7th Edition                     April 27, 1985                       UPDATE(8)