While these days the systemd based timesync* things are doing most of
the work there is still a lot of buzz around the automated ntpdate on
ifup. I'll try to to summarize the outcome of multiple discussions and
bugs around this and propose a solution.
- I've seen various reports of ntpdate syncing too much or time changes due to
that annoying people.
- but then there are different user scenarios so some want and others won't
"autoupdate" feature on ifup
- the ones that want it disabled are usually only "inconvenience issues" like
too much calls, but also cases like "know it will hang", so could I disable it
in advance
- the ones require the updates are mostly having more severe issues (like
breaking authentication due to time being off afterwards)
We should try to create a solution for both parties to be able to config the
system to their way.
So lets keep the default to sync (as it seems the more critical way), but
provide a way to disable it via the config files.
Doing it via an environment variable also allows to "overwrite" it in ifup
calls like
DISABLE_NTPDATE=1 ifup eth0
The config file has to be read in ntpdate-debian if the variable is not
set.
Then just a simple check for that variable in the script to exit if disabled:
[ "${DISABLE_NTPDATE:-0}" != "0" ] && exit 0
So the behavior would be like:
1. default it is running on ifup
2. one could set a different default in the config file
3. one can overwrite whatever was set via an environment variable
... creating a patch for that and providing to Debian for a latter sync.
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https://bugs.launchpad.net/bugs/1206164
Title:
/etc/network/if-up.d/ntpdate does not detach correctly
Status in ntp package in Ubuntu:
Triaged
Bug description:
It seems that the intent of /etc/network/if-up.d/ntpdate is to
background itself, as it creates a subshell with &.
As reported in bug 1202758, this doesn't seem to work correctly. That
doesn't close the file descriptors. As a result, if something is
waiting on the output of 'ifup', it will sit and wait until ntpdate is
finished.
Example:
$ time sudo sh -c 'o=$(sh -c "ifdown eth0 ; ifup eth0" 2>&1) ; echo $o'
If we change the way it detaches itself to close stdout, stdderr, and
stdin, then we're fine.
I'm reporting this, but I'm not sure how much of a real problem it is. As if
th
e command sends stdin and stdout to /dev/null, then debugging its output
would b
e more difficult.
Example diff:
$ diff -u /etc/network/if-up.d/ntpdate.dist /etc/network/if-up.d/ntpdate
--- /etc/network/if-up.d/ntpdate.dist 2013-07-29 15:47:54.242781947 +0000
+++ /etc/network/if-up.d/ntpdate 2013-07-29 15:48:06.946781947 +0000
@@ -56,4 +56,4 @@
lockfile-remove $LOCKFILE
fi
-) &
+) </dev/null >/dev/null 2>&1 &
ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: ntpdate 1:4.2.6.p5+dfsg-2ubuntu2
ProcVersionSignature: User Name 3.10.0-5.15-generic 3.10.2
Uname: Linux 3.10.0-5-generic x86_64
ApportVersion: 2.11-0ubuntu1
Architecture: amd64
Date: Mon Jul 29 15:32:30 2013
MarkForUpload: True
ProcEnviron:
TERM=xterm
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: ntp
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.network.if.up.d.ntpdate: 2013-07-29T15:32:03.567775
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