On 6/27/2022 12:48 AM, Thomas Haller wrote:
On Fri, 2022-06-24 at 17:39 -0700, Jim Garrison via networkmanager-list
Simple question: Where does NetworkManager keep the lease data so it
knows when it needs to renew the lease?


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

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
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