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Re: NFS--mounted builddirs and detecting clock skew

From: Harlan Stenn
Subject: Re: NFS--mounted builddirs and detecting clock skew
Date: Thu, 22 Nov 2007 00:33:08 +0000

Bob Friesenhahn wrote:
> On Wed, 21 Nov 2007, Harlan Stenn wrote:
> >
> > A variety of problems can crop up if one is "doing things" in an
> > NFS-mounted filesystem and there is clock skew between the local machine
> > (NFS client box) and the machine that hosts the  actual filesystem (NFS
> > server box).
> I suggest that you check out some cool software called xntp which can 
> help correct your clock skew problems.

Good idea - thanks!  Where might I learn more?

More to the point, I'm discussion an issue separate from NTP.  I am
trying to *detect* an existing problem condition, not prevent the

> > If I am running a configure script and there is a clock skew problem, I
> > would want to know this ASAP beacuse if the clock skew is not
> > deliberate, I want to fix it Right Away.
> Which particular clock skew do you want to detect?
>    * Clock skew to source directory
>    * Clock skew to build directory
>    * Clock skew to header files outside the source directory
>    * Clock skew to libraries outside the build directory
>    * Clock skew to temporary file directory (gasp!)
>    * Clock skew due to filesystem with 1 second time resolution
>    * Clock skew during build due to wandering clock
>    * Clock skew to parallel build machine
> All of these problems are possible.  Some issues are seen by GNU make 
> and others are not.

I *think* I'd be happy with 'clock skew in the build directory'.

If there are ways to use the same core functionality to measure the
other cases you metion, that would be great.

> When my clocks are a bit off I have noticed that 
> GNU make sometimes intermittently complains due to the "wandering 
> clock" problem.

I don't see 'wander' (case insensitive) in either the gmake 3.81 or
3.79.1 source trees.

> If I am not imagining things, I have seen configure 
> complain about clock problems before so perhaps there is already a 
> sanity check in place.

AM_SANITY_CHECK will test to see if a newly-created file is older than
distributed files, but that is more of a system clock check than a clock
skew check.


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