Re: systemd/dhcp v. ntpd
On Wed, Feb 09, 2022 at 05:44:25PM +0300, Reco wrote:
> Hi.
>
> On Wed, Feb 09, 2022 at 09:05:51AM -0500, Lee wrote:
> > On 2/8/22, Greg Wooledge <greg@wooledge.org> wrote:
> > > On Tue, Feb 08, 2022 at 02:43:02PM -0500, Lee wrote:
> > >> How to tell systemd to leave the ntpd config alone?
> > >
> > > What makes you think the two are connected in any way?
> >
> > $ grep "Network Time Service" syslog
> > Feb 6 12:06:48 spot systemd[1]: Stopping Network Time Service...
> > Feb 6 12:06:48 spot systemd[1]: Stopped Network Time Service.
> > Feb 6 12:06:48 spot systemd[1]: Starting Network Time Service...
> > Feb 6 12:06:48 spot systemd[1]: Started Network Time Service.
> > Feb 6 12:09:25 spot systemd[1]: Stopping Network Time Service...
> > Feb 6 12:09:25 spot systemd[1]: Stopped Network Time Service.
> > Feb 6 12:09:25 spot systemd[1]: Starting Network Time Service...
> > Feb 6 12:09:25 spot systemd[1]: Started Network Time Service.
> > Feb 6 12:22:53 spot systemd[1]: Stopping Network Time Service...
> > Feb 6 12:22:53 spot systemd[1]: Stopped Network Time Service.
> > Feb 6 12:22:53 spot systemd[1]: Starting Network Time Service...
> > Feb 6 12:22:53 spot systemd[1]: Started Network Time Service.
> > ... etc
> >
> > every time I connect or disconnect from a wifi network.
>
> Or it could mean that dhclient hook merely asks systemd to restart ntpd
> service. See /etc/dhcp/dhclient-exit-hooks.d/ntp.
What a disaster. The number of moving parts here is just staggering.
OK, now we know that the real culprit is in fact Debian's concept of
how a DHCP client should behave. Let's try to track down all of the
pieces and figure out what the *best* answers are.
The first piece, we now know, is the /etc/dhcp/dhclient-exit-hooks.d/ntp
script. We can see that this creates a temporary file, writes a new NTP
configuration into it, moves it to /run/ntp.conf.dhcp and then asks the
system to restart ntpd.
The second piece is the /etc/init.d/ntp script (SURPRISE! sysv-rc still
lives!). Here we see this bit of conspiracy:
if [ -e /run/ntp.conf.dhcp ]; then
NTPD_OPTS="$NTPD_OPTS -c /run/ntp.conf.dhcp"
fi
If /run/ntp.conf.dhcp exists, then it's used preferentially over the
system's *real* ntp.conf file. So, the DHCP hook generates this fake
config file, and then the sysv-rc script sees it and decides to use it.
AND SOMEONE THOUGHT THIS KLUDGE WAS A GOOD IDEA!!
So, this gives us at least two points of attack. You could edit the DHCP
hook script, and stop it from creating the fake config file. Or, you
could edit the sysv-rc script and stop it from *respecting* the fake
config file.
The question, I suppose, is which one of these is less likely to be
overwritten if the ntp package is updated. But they are both listed in
/var/lib/dpkg/info/ntp.conffiles so they should both survive a package
update. (You'll be asked whether to keep the existing file, etc.)
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