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From: jfc@athena.mit.edu (John F Carr)
Newsgroups: comp.unix.wizards,comp.sys.att
Subject: Re: 6386 shutdown: I CAN'T BELIEVE at&t was really this stupid!
Message-ID: <12044@bloom-beacon.MIT.EDU>
Date: 16 Jun 89 07:53:15 GMT
References: <483@oglvee.UUCP> <14401@bfmny0.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: jfc@athena.mit.edu (John F Carr)
Organization: Massachusetts Institute of Technology
Lines: 36

In article <14401@bfmny0.UUCP> tneff@bfmny0.UUCP (Tom Neff) writes:

>To minimize the risk from power hits and crashes, I add a root cron job
>that performs a 'sync ; sync' every 10 minutes.  I have not been reliably
>persuaded that this is something the kernel does automatically on V/386,
>although I know of UNIXen where that's true.

We have the following man page (and a program to go with it) on our BSD 4.3
system.

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

NAME
     update - periodically update the super block

SYNOPSIS
     /etc/update [-n]

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.

     Normally, update opens certain system directories to keep
     them in the name translation cache.  If the -n option is
     given, subdirectories of /usr are not opened so that remote
     system libraries can be unmounted while the system is run-
     ning.


It doesn't appear to place much load on a system to do this twice
per minute (perhaps 2 minutes CPU per day of runtime).

    --John Carr (jfc@athena.mit.edu)