On 2009-05-15 18:20, Guy Harris wrote:
On May 15, 2009, at 12:43 AM, Jefferson Ogata wrote:
This has come up before, back when we were talking about the NG format.
I guess I got confused by the current context; if pcap files are
natively UTC (which I had thought they were until this thread arose,
seeming to suggest they weren't), great.
They are.
The issue in the thread is how to *display* the time stamps, especially
if you want to know what *local* time, at the point of capture, a packet
arrived, when you're reading it in a different time zone. *That*
requires that some form of time zone information for the point of
capture be available, whether in the capture file or, for example, in an
email to which the capture file was attached. So there's a use for time
zone information in a capture file even when the time stamps in the
capture file are in UTC.
It seemed to me as if he was trying to go the other way 'round. I don't
have the original message any more so I can't say why I got that impression.
I configure all my systems in
UTC anyway, so I never have issues, and I wouldn't be able to tell
without tweaking $TZ.
Frankly, I don't understand why anyone configures a UNIX-like system in
anything other than UTC. That's what $TZ is for.
There are two ways I see in which "configure a UNIX-like system for a
particular time zone" could be read:
1) set the default time zone used by routines such as localtime()
and mktime() to convert UTC to local time;
2) set the time zone of the value returned by
time()/gettimeofday()/etc..
3) Set the time zone of the system to a local zone instead of UTC, e.g.
by setting a global TZ value or copying an Olson zone file to
/etc/localtime. This is what a lot of people do, and I don't see why.
Users who want their desktops to operate in a local zone can just set TZ
for their environment.
One thing I hate having to deal with is syslog messages logged in a
local time zone. There is no indication of zone in syslog messages.
Furthermore, at DST end you can have syslog messages where it is
impossible to determine the actual time something was logged.
Correlating syslog messages from multiple systems is a royal PITA when
people use local zones system-wide, and it's completely unnecessary to
do so.
Anyway, this is off-topic. But as someone who has to correlate data from
systems in 12 or so different time zones, it's something I care about.
--
Jefferson Ogata <[email protected]>
NOAA Computer Incident Response Team (N-CIRT) <[email protected]>
"Never try to retrieve anything from a bear."--National Park Service
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