Running Circles Around Detecting Containers

Recently my monitoring service warned me that my Raspberry Pi was not syncing its time any more. I logged into the devices and tried restarting systemd-timesyncd.service and it failed.

The error it presented was:

ConditionVirtualization=!container was not met

I was confused. Although I was running containers on this device, this was on the host! 😯

I checked the service definition and it indeed had this condition. Then I tried to look up the docs for the ContainerVirtualization setting and found out Systemd has a helper command that can be used to find out if it has been run inside a Container/VM/etc.

To my surprise running systemd-detect-virt determined it was being run inside a Podman container, although it was run on the host. I was totally confused. Does it detect any Container or being run in one? 😵‍💫

I tried to dig deeper, but the docs only tell you what known Container/VM solutions can be detected, but not what it uses to do so. So I searched the code of systemd-detect-virt for indications how it tried to detect Podman containers … and I found it: it looks for the existence of a file at /run/.containerenv. 😯

Looking whether this file existed on the host I found out: it did!!! 😵 How could this be? I checked another device running Podman and the file wasn’t there!?! 😵‍💫 … Then it dawned on me. I was running cAdvisor on the Raspberry Pi and it so happens that it wants /var/run to be mounted inside the container, /var/run just links to /run and independent of me mounting it read-only it creates the /run/.containerenv file!!! 🤯

I looked into /run/.containerenv and found out it was empty, so I removed it and could finally restart systemd-timesyncd.service. The /run/.containerenv file is recreated on every restart of the container, but at least I know what to look for. 😩

Naïvité FTW

Daniele Procida explores how a certain naivety (being unsophisticated) can lead to beautiful and useful things.

Update 2021-08-15: the original video from DjangoCon 2018 is not available any more. It seems Daniele gave a similar talk at EuroPython 2018 also.

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Exciting Unlimited Register Machines

A brief and entertaining talk by an obviously excited presenter. 🙂 It goes into the same directions as Jim Weirich’s talk about the Y combinator.

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AR create_with

I knew there was AR’s


  method but I didn’t know it had a very useful companion



@something ||= SomeModel.create_with(some: "stuff").find_or_create_by(foo: "bar")

This will either find a record 

SomeModel.where(foo: "bar")

  or create it with

SomeModel.create(foo: "bar", some: "stuff")

 . Very useful.