Yesterday I wrote about restarting or redoing something after a systemd service restarts . The non-hypothetical situation that caused me to look into this was that after we applied a package update to one system, systemd-networkd on it restarted and wiped out some critical policy based routing rules. Since I vaguely remembered this happening before, I sighed and arranged to have our rules automatically reapplied on both systems with policy based routing rules, following the pattern I worked out .

Wait, two systems? And one of them didn't seem to have problems after the systemd-networkd restart? Yesterday I ignored that and forged ahead, but really it should have set off alarm bells. The reason the other system wasn't affected was I'd already solved the problem the right way back in March of 2024, when we first hit this networkd behavior and I wrote an entry about it .

However, I hadn't left myself (or my co-workers) any notes about that March 2024 fix; I'd put it into place on the first machine (then the only machine we had that did policy based routing) and forgotten about it. My only theory is that I wanted to wait and be sure it actually fixed the problem before documenting it as 'the fix', but if so, I made a mistake by not leaving myself any notes that I had a fix in testing. When I recently built the second machine with policy based routing I copied things from the first machine, but I didn't copy the true networkd fix because I'd forgotten about it.

(It turns out to have been really useful that I wrote that March 2024 entry because it's the only documentation I have, and I'd probably have missed the real fix if not for it. I rediscovered it in the process of writing yesterday's entry .)

I know (and knew) that keeping notes is good, and that my memory is fallible. And I still let this slip through the cracks for whatever reason. Hopefully the valuable lesson I've learned from this will stick a bit so I don't stub my toe again .

(One obvious lesson is that I should make a note to myself any time I'm testing something that I'm not sure will actually work. Since it may not work I may want to formally document it in our normal system for this , but a personal note will keep me from completely losing track of it. You can see the persistence of things 'in testing' as another example of the aphorism that there's nothing as permanent as a temporary fix.)