Someone asked this question in one of his blog posts:

Yes, I’m seeing something like that now in the my dhdcp logs. Here is the actual message:

I think I know why this happened. Basically, the machine with MAC address of ’08:00:27:6e:61:b8′ used to have grab an IP address

from the pool. Then later on, I have created a reservation for it.

On Centos 7, the lease file is located at: /var/lib/dhcpd/dhcpd.leases. Here’s the duplicated lease for mathtXXX:

By removing the above block and restarting dhcpd service, the “uid lease duplicate” message no longer appears in the log.