Groups | Search | Server Info | Login | Register

Groups > comp.os.linux.development.system > #353

Re: Getting time of last reboot on Linux

Cross-posted to 2 groups.

Show key headers only | View raw

Lew Pitcher <lpitcher@teksavvy.com> wrote:
<snip>
> Question: how likely is your scenario? That is, in (say) 1000 reboots of an
> aribtrary machine, how often would NTP radically reset the system clock?

I don't know. Perhaps it's not something to worry about. But "arbitrary
machine" is a significant qualification.

I worked at an appliance company once where a component manufacturer sent
thousands of NICs with identical MAC addresses. The company wasn't equipped
to reflash the NICs individually, so we had to do it in the appliance
firmware. And in any event, certainly this wasn't the first time a huge
batch of such NICs left the factory, so it was probably prudent to handle
this condition anyhow. If somebody asked me the question how often would I
truly need to worry about duplicate MAC addresses I'd have to respond, "all
the time!"

Imagine a run of appliances or motherboards with a bad RTC. The answer could
again be, "all the time!" But perhaps this is common enough to actually be
worrisome without such a pathological scenario.

I've also seen cases where vendors run `ntpdate -b` from a cron job rather
than relying on ntpd to skew the clock, or where ntp isn't used regularly at
all. It's one thing when writing software to rely on the expertise and
sanity of developers whose aim is correctness. It's another thing entirely
to rely on vendors whose aim is to maximize profit, a pursuit which heavily
discounts correctness. Most vendors (by number) rely on _other_ people doing
the correct thing, then writing crappy software on top of that.

I suspect these sorts of clock issues tend to manifest as odd errors that go
away quickly enough that nobody bothers to investigate. Imagine a software
watchdog that restarts an HTTP service because the clock jumped forward 10
seconds. The wrong thing happened, but it was rather benign because HTTP is
stateless and the user habitually resubmitted the form.

Back to comp.os.linux.development.system | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Getting time of last reboot on Linux Alex Vinokur <alex.vinokur@gmail.com> - 2011-12-18 09:35 -0800
  Re: Getting time of last reboot on Linux Steve Thompson <smt@vgersoft.com> - 2011-12-18 12:46 -0500
    Re: Getting time of last reboot on Linux Alex Vinokur <alex.vinokur@gmail.com> - 2011-12-18 10:12 -0800
      Re: Getting time of last reboot on Linux Volker Birk <bumens@dingens.org> - 2011-12-18 18:19 +0000
        Re: Getting time of last reboot on Linux Andrew Smallshaw <andrews@sdf.lonestar.org> - 2011-12-21 16:01 +0000
  Re: Getting time of last reboot on Linux Volker Birk <bumens@dingens.org> - 2011-12-18 18:18 +0000
  Re: Getting time of last reboot on Linux Lew Pitcher <lpitcher@teksavvy.com> - 2011-12-18 13:31 -0500
    Re: Getting time of last reboot on Linux Stephane CHAZELAS <stephane_chazelas@yahoo.fr> - 2011-12-18 21:48 +0000
      Re: Getting time of last reboot on Linux Barry Margolin <barmar@alum.mit.edu> - 2011-12-18 21:29 -0500
        Re: Getting time of last reboot on Linux Stephane CHAZELAS <stephane_chazelas@yahoo.fr> - 2011-12-19 12:59 +0000
    Re: Getting time of last reboot on Linux William Ahern <william@wilbur.25thandClement.com> - 2011-12-19 15:15 -0800
      Re: Getting time of last reboot on Linux Lew Pitcher <lpitcher@teksavvy.com> - 2011-12-19 19:20 -0500
        Re: Getting time of last reboot on Linux William Ahern <william@wilbur.25thandClement.com> - 2011-12-19 18:32 -0800
        Re: Getting time of last reboot on Linux gordonb.xm1tg@burditt.org (Gordon Burditt) - 2011-12-22 00:16 -0600
          Re: Getting time of last reboot on Linux Stefan Monnier <monnier@iro.umontreal.ca> - 2012-01-09 09:18 -0500
      Re: Getting time of last reboot on Linux Ivan Shmakov <oneingray@gmail.com> - 2011-12-20 11:48 +0700
  Re: Getting time of last reboot on Linux Richard Kettlewell <rjk@greenend.org.uk> - 2011-12-21 17:06 +0000
    Re: Getting time of last reboot on Linux gazelle@shell.xmission.com (Kenny McCormack) - 2012-02-09 17:25 +0000
      Re: Getting time of last reboot on Linux Richard Kettlewell <rjk@greenend.org.uk> - 2012-02-09 21:11 +0000

csiph-web