Uhm...what's this? [rdate question]

[Matthew Saltzman]

On Mon, 5 Apr 2004, Brian Fahrlander wrote:

> On Mon, 2004-04-05 at 11:33, Tom 'Needs A Hat' Mitchell wrote:
>
> > At the end of an strace of rdate -s time.nist.gov I see:
> >
> >   5863  connect(3, {sa_family=AF_INET, sin_port=htons(37), sin_addr=inet_addr("192.43.244.18")}, 16) = ? ERESTARTSYS (To be restarted)
> >   5863  --- SIGALRM (Alarm clock) @ 0 (0) ---
> >   5863  +++ killed by SIGALRM +++
> >
> > I suspect that there is a time-out built into rdate that is getting
> > triggered.  Since this the weekend that daylight saving time switched
> > here I bet the site was being hit bunches.
> >
> > I guess I could look at the source and ... naw guessing
> > is too much fun.  ;-)
>
>     Good man! You found a reason where once there was none.  Kudos.
>
>     Will the source, though, say why they picked "Alarm clock" as a
> diagnostic instead of "Time source overloaded" or "Time not available"?

Got me curious, so I poked around a little bit.

The message appears to come from the SIGALRM implementer.  (The string
"Alarm clock" appears nowhere in the rdate binary.)  SIGALRM is a
general-purpose POSIX timeout signal--see alarm(2).  It can be used, for
example, to implement the sleep(3) function and other things.  So the fact
that you are getting the message from a clock-related program is a mere
coincidence.

>
>     Hackers.  Good or bad, they're always a couple of degrees askew from
> the rest of the world.  :>

Bless 'em!
-- 
		Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs