Restarting DHCP safely whilst avoiding partner-down state

Chuck Anderson cra at WPI.EDU
Fri May 13 18:02:27 UTC 2016


On Fri, May 13, 2016 at 04:02:23PM +0100, Terry Burton wrote:
> On 13 May 2016 at 15:57, Chuck Anderson <cra at wpi.edu> wrote:
> > On Fri, May 13, 2016 at 03:23:25PM +0100, Terry Burton wrote:
> >> On 13 May 2016 at 14:22, Chuck Anderson <cra at wpi.edu> wrote:
> >> > I don't know if a corrupted lease file would cause a failure to start
> >> > the dhcp server, or if it would just go unnoticed, perhaps with a log
> >> > message.  But like I said, we've never had a failure to start the
> >> > server that was caused by a lease file issue.
> >>
> >> In our experience leases files corrupted by other means can cause a
> >> failure to start. I don't recall whether that was due to mere
> >> truncation though...
> >
> > There is also the -T parameter to test the lease file:
> >
> >        The -T flag can be used to test the lease database file in a similar way.
> >
> > It might be a good idea to also use this test before restarting.
> > While it won't fix a corrupted lease file, it may prevent you from
> > losing all DHCP service due to a failure to restart.
> 
> I think this will require the leases file to be closed at the point of
> testing, i.e. the daemon has already exited.
> 
> For the more general issue with systemd verifying the configuration
> see: https://lists.freedesktop.org/archives/systemd-devel/2016-May/036481.html

Is there a way to signal dhcpd to write out the lease file so it can
be checked?

It seems that dhcpd needs a journaling mechanism similar to named,
where it writes the changes to a .jnl file and periodically
incorporates those changes into the main zone file.


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