au QuaStation - Part 12 - More Tips & Tricks

 

Netplan and Resolved

These aren't really QuaStation specific, just general stuff for headless Ubuntu server machines in static environments.  

Ubuntu, in their infinite wisdom, decided to make breaking changes to the way the network is configured, even on the server releases.  I understand wanting to have a more dynamic system for end user machines, especially laptops, but removing ifupdown in a non-compatible way is just wrong because it breaks existing scripts, etc.  

I wouldn't mind the change if it was unquestionably better, and retained compatibility - but unfortunately netplan is neither of those things.  It seems to be change for the sake of change.  

If, like me, you are not accepting of this change, you can follow the link below to see how to disable and neuter "netplan".  

https://askubuntu.com/questions/1031709/ubuntu-18-04-switch-back-to-etc-network-interfaces

Note that you may have to change or modify "resolved" as well.  I have found that when DNS resolution is not working on Ubuntu, resolved is normally the culprit.  

There is a good discussion of the resolved situation here:

https://askubuntu.com/questions/907246/how-to-disable-systemd-resolved-in-ubuntu

Avahi Issues

Avahi sometimes just doesn't work, so you can get resolution errors.  Of course you could always check your router to find an IP assigned by DHCP - and an even more certain way is to assign IPs statically to each machine - but it's nice to be able to use hostnames without having to edit a static hosts file on every machine.  

I have found that restarting Avahi always solves the issue - but why not be more proactive and add a avahi-restart script to the /etc/cron.hourly/?  Doing this has completely eliminated the issue for me.  

More fun with LEDs

/sys/class/leds/led_ctrl1/brightness - Controls the brightness of all of the LEDs.

/sys/class/leds/led_ctrl/brightness - Same as above.

There doesn't seem to be a difference in how these two operate - both appear to do exactly the same thing.

Setting to 0 dims the LEDs, while setting to 1 (or higher) sets them to maximum brightness.  

Setting the brightness doesn't affect whether that LED is on or off, so you could, for example, have a cron job to set them to low brightness at night time, and back to full brightness during the day time.  (Many home WiFi routers have similar functionality).