Public bug reported:
Binary package hint: ntpdate
I was testing Xen with the network-bridge networking script under xend,
using a system in a locked-off test network. The system was unable to
reach ntp.ubuntu.com, and kept exhibiting peculiar behavior when setting
up the bridge:
The bridge script would ifdown eth0, set up peth0 and xenbr0 and vif0
devices, and wait in a sleep-loop for them to be ready. When it found
peth0 to be satisfactory, it tried to do an "ifup eth0" but every time
it did ifup would complain that eth0 was already up. Upon booting, I
would check ifconfig eth0, and it would be configured but neither UP nor
RUNNING. However, /var/run/network/ifstate contained an "eth0=eth0"
line.
After verifying with /usr/bin/strings that ifupdown was indeed the
only tool involved that touches /var/run/network/ifstate, I inserted
some ps|grep pipelines into the network-bridge xend script. Lo and
behold, there was a pre-existing ifup process from
/etc/init.d/networking that stayed around from the beginning of the
network-bridge invocation right up through the first few seconds of the
peth0 sleep-loop. When it exited, it checkpointed the ifstate file with
outdated information, confusing the ifup in the network-bridge script.
It turns out that the cause of this was ntpdate, which did not
background once it forked out of the ifup process (which *had*
backgrounded). Since it couldn't reach ntp.ubuntu.com, it kept ifup
open long enough that when it closed, it almost consistently trampled on
my network-bridge process.
Please make ntpdate run in the background in the if-up.d/ script, so
that ifup is at least a *little* closer to atomic.
** Affects: ntp (Ubuntu)
Importance: Undecided
Status: Unconfirmed
--
ntpdate holds ifup open if it cannot reach a server, catastrophically delaying
ifstate writes
https://launchpad.net/bugs/81145
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