Running systemd inside a Centos 8 Docker container

Support for systemd in Docker has improved a lot since this 2016 article, but it’s still not obvious quite how to make it work. Why would you want this? Mostly for testing full-server deploys (for example we test ansible deployments against various docker containers to ensure there are no bugs).

Here’s a systemd-based centos 8 Dockerfile that also includes an ssh server:

You can then launch this like:

For the latest centos 7 you can use the following Dockerfile:

Complex network setup on Centos/Redhat 8 via Network Manager

Here are some notes, mostly for my future self about how to set up bond + vlan + bridge networks in Centos 8 in order to create a highly resilient virtual machine host server.

Firstly, create the bond interface and set the options:

Note the 802.3ad option – this says we are going to be using the LACP protocol which requires router support, however you can look at the different mode options in the kernel documentation.

Then, we add the required interfaces into the bond – in this case enp131s0f0 and enp131s0f1

If you want to create a standard vlan interface over the top of the bond for vlan tag 123 we can do this just with 1 more command:

Alternatively if you want to set up a bridge on this interface:

If you don’t want the default route or DNS, simply remove the ipv4.gateway and ipv4.dns options above.

If you want to create a bridge which doesn’t have any IP address on the host (just bridges through to the host vm’s) then replace all the ipv4 settings with: ipv4.method disabled ipv6.method ignore.

Ripping unfinalized DVDs from Linux

Recently we had some DVD’s with old family videos that had been recorded directly but never finalized, the device that recorded them then broke so it was impossible to finalize them, and it seemed to be pretty much impossible for anything else to read them. So, I figured out a way to recover them using linux…

First I installed the dvd+rw-tools package on ubuntu and used that to get various info and prove that the DVD itself was readable even though nothing on the system could see it as a video disk or filesystem.

I then pulled the entire DVD into a file on the local computer for easier processing later. The command will produce lots of errors (as there are parts of the DVD that are not readable as they were never written to), but the output file (image.iso) will contain a full dump of the DVD eventually

I then put together a short perl script to search through this file for 1kb blocks beginning with the magic tag DVDVIDEO – these seemed to be the starts of individual chapters, which avconv (also called ffmpeg on some distributions) can then extract into proper video/audio.

Save that as extract_dvd_tracks.pl and then run it to extract them as files named like out0.mp4. Note that it won’t process tracks that are less than about 1Mb because there seemed to be a number of small sections like this which we wanted to skip over.

Job done! Note that there are probably many different formats and layouts for unfinalized DVD’s, this may be just one of many but hopefully the principle remains the same.

Extracting all PHP code from a file

In checking over a project recently, I wanted to extract all PHP code from a set of files and combine it into a single output so I could easily assess what was being used. The eventual command I ended up with was as follows, hopefully it will be useful to someone else in the future:

Implementing correct modal navigation with react-router

I’ve recently been converting a big project from jquery mobile into React and Material-UI. One area that seems pretty weak compared to other frameworks is with regards to having a proper mobile-focused infrastructure for navigation. One of the big issues for me was that of modals (for example a dialog, alert or popup page components). For example when you see an alert you want to be able to click on the ok button to dismiss it. If you are on android you also expect to be able to press the back button to dismiss. However if you have separate routes for your modals such that the url changes when they are open, if you refresh the page at that point you will have a modal but no previous state to explore. There seem to be certain hacks with react-router-dom which allow you to change the page but keep the URL the same, assuming you are using BrowserRouter, however because this was a legacy project I want to keep on using HashRouter. So, I whipped up a quick HOC hack to wrap around a modal which will allow both the back navigation to work as expected, and also for refreshes to go to the main page rather than opening the modal.

I already had a standard base class which had the handleClose() method to close off a dialog and signal to the parent that it was done, so I expanded it to include a state listener as below

You then just wrap your component with this – for example

This works because react-router-dom doesn’t attempt to parse query strings etc, so when the app is first loaded you want to just have something to remove any of the ?dialog path hacks: