Re: Where does NetworkManager keep DHCP client lease data?

[Jim Garrison <jhg jhmg net>]

On 6/27/2022 12:48 AM, Thomas Haller wrote:
> On Fri, 2022-06-24 at 17:39 -0700, Jim Garrison via networkmanager-list
> wrote:
[snip]
> > Simple question: Where does NetworkManager keep the lease data so it
> > knows when it needs to renew the lease?
>
>
> Hi,
>
>
> the files in /var/lib/NetworkManager are internal not public API. That
> of course does not prevent you from accessing it, but use with care.
> That is also the case for the dhclient lease files. These files are not
> supposed to give information about the lease.
>
> You can see the current lease information on the D-Bus API, for example
> via `nmcli -f ALL device show ens1` or `nmcli -f DHCP4 device show
> ens1`.
>
> In recent NM versions, you can also find the same information in
> `/run/NetworkManager/devices/$IFINDEX` (if you prefer reading files).
> This *is* public API.
>
>
> A lease only makes sense to NetworkManager while it's running and
> connected. It just knows in memory how long the lease is valid. I don't
> think that works different when you use dhclient alone (not as
> NetworkManager plugin). Well, maybe you could restart dhclient, and it
> would have remembered that it had a lease. NM doesn't do that. If you
> re-activate the device (or reboot or restart NM), it will try to get a
> new lease and start the DHCP state machine again. It only uses the
> previous ADDRESS= to give a hint to the DHCP server which address it
> would like to have.
>
>
> If the device is currently not active, then there is no public API for
> past leases. Yes, you could parse the
> /var/lib/NetworkManager/*.lease to get some some of the information,
> but this only contains information which NetworkManger cares about (the
> `ADDRESS=`), not most of the interesting data. It's anyway not clear
> what you would like to know about past leases.

I was trying to debug a problem with a DHCP server.  Having worked in
the past with dhclient, I was expecting to find the lease time stored
somewhere, but couldn't find it.

Thanks for clarifying the use of nmcli to examine the current lease.

--
Jim Garrison
jhg acm org