udev "database"

Leroy Tennison leroy at datavoiceint.com
Thu Sep 13 22:11:26 UTC 2018

We created /etc/udev/rules.d/70-persistent-net.rules under Ubuntu 14 and later upgraded to Ubuntu 16.  We have rebooted numerous times and the name-to-MAC-address mapping continued to be applied.  However, one of the units we were using this on failed and we did a chassis replacement (kept the original hard drive).  Even after editing the MAC address values in the rules file, the mappings were no longer applied at boot.  I learned that the format changed between Ubuntu 14 and 16 and that the old format no longer worked (had to remove the KERNEL== ..." parameter from each line).

What bothers me is why the old file format still works on existing Ubuntu 16 systems and what kinds of other things might break that.  Somehow there must be a "database" (I use the term in the loosest sense possible) or scheme which says in effect "if nothing has changed use the previous values".  How does this work and does it work differently under netplan?

Thanks for your help.

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Leroy Tennison
Network Information/Cyber Security Specialist
E: leroy at datavoiceint.com
2220 Bush Dr
McKinney, Texas
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