[mrtg-developers] Suggestion for improvement

Alex van den Bogaerdt alex at ergens.op.het.net
Mon Dec 1 13:59:34 MET 2003


Every now and then someone's clock is set wrong.  This can have a
serious impact on MRTG.

My suggestion is to set a limit on what MRTG accepts as an interval
without updates.

For example:

It is december 1st, 2003, 12:46 UTC.  For whatever reason the clock is
set wrong, it is set to Januari 29th 2004.

Currently MRTG (and RRDtool for that matter) will happily fill the
interval between the real now and the supposed now.  This is bad,
because there's no way back (besides restoring file from backup).

What if there was a limit, say 10 times the expected interval.
Two situations may occur:

a) The clock is wrong; the user wants MRTG to stop
b) The clock is set OK; the user wants MRTG to continue

I think in case (a) the user can correct the clock and MRTG will
continue to operate as expected, after maybe loosing a couple of
updates.  This may produce a gap but this is not too serious.

In case (b), the user will probably know that MRTG was stopped (for
whatever reason) and the user could signal this to MRTG by setting
a special flag or so.

If this mechanism would be included in MRTG, it could be configurable,
for instance:

    Options[myrouter]: checktime
    Heartbeat[myrouter]: 3000
(meaning: 10*300 seconds).

If this option is set, MRTG refuses to continue if the clock is too
far ahead.  When the uses really wants MRTG to continue a simple
comment before this line and a restart of MRTG is enough.

I'm not able to program this myself (lack of skill _and_ lack of time).
I hope someone will pick this up and improve the program.


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