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Re: "Clock skew" error...

On 23 Nov, Paul J Thompson wrote:
> Hi.
> A friend I hAve been helping with Linux has been having this funny
> error when compiling things with gcc.  It says:
> make: *** Warning:  Clock skew detected.  Your build may be incomplete.
> What the heck does this mean?  (kinda amusing but just not very nice...)

Clock skew is a nasty feature of NFS networks, where the system clocks
on two machines with shared directories differ.  What then happens is
that when make runs it creates timestamps on object files that don't
necessarily reflect the sequence of events.  For example, imagine that
machine A has a directory NFS-mounted from machine B, but that A's
clock runs five minutes behind B's.  You can then have the following
sequence of events:

	Build software from machine B
	Update foo.c on machine A (takes < 5 minutes)
	Remake software - nothing happens.

I don't know how make detects the clock skew, but I suspect it's
noticed that one or more files are dated in the future (from machine
A's perspective).  So this warning might possibly be caused if you've
changed the system time recently.

The usual cure for NFS-triggered clock skew is to run xntpd.  You can
also work around it by doing a "make clean; make".

Hope that helps,
M a l c . . .            |  "A wrong parameters may be caused the mainboard
(malc@thing.demon.co.uk) |   out of order."  -- Pentium motherboard manual.

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