[tcpdump-workers] Should the tcpdump tests be run with TZ=GMT0, or should the AFS printer print time stamps in UTC?

John Hawkinson jhawk at MIT.EDU
Sun Aug 5 13:21:47 EDT 2018

Denis Ovsienko <denis at ovsienko.info> wrote on Sun,  5 Aug 2018
at 17:05:20 +0100 in <1650ad5fd29.b5d2798f311917.536858429581803402 at ovsienko.info>:

> It works in an interactive session; but as soon as the output makes
> it to the Internet and stays there long enough, people will no
> longer understand what the printed time was in their local time or
> UTC. The value of TZ influences the output, but remains invisible.

I think this is not a real problem; in practice it's rare that long-lived non-.pcap tcpdump decodings have significant meaning associates with the time zone of time outputs from printers. One could imagine printing the local time zone adjacent to the "listening on" output at startup, but it seems unnecessary.

But it's important not to let theoretical issues make the tool worse for actual users.

> I understand what you are suggesting, and your description is
> correct, but it does not solve the problem of interpreting tcpdump
> output correctly in a place or time different from the
> original. That said, I can live with print-rx.c using local time and
> being imperfect, it has worked like this many years. Still, I think
> local time should not be the norm for other decoders.

Doesn't this argument apply for other decoders as well? Whatever is done should not make the output of decoders harder for the diagnostic users of tcpdump to interpret, or unnecessarily change the output format.

One could imagine having all of these printers respect -tt, &c., and conceivably adding an option to force decoder time printing to be UTC; but such an option would be tantamount to setting TZ=UTC, and generally the Unix Way is not to duplicate such OS functionality.

p.s.: Using GMT or GMT0 is deprecated, please use UTC instead.

--jhawk at mit.edu
  John Hawkinson

More information about the tcpdump-workers mailing list