Configuring a Surveillance Camera with Udev and Systemd
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© Photo by Shaurya Sagar on Unsplash
You can use systemd to make your computer react when you change a file or plug in a device. We'll show you how to leverage these powerful features to build a surveillance system.
In modern Linux systems, the Udev device manager listens for notice of new devices added to the system. If a device is detected, Udev can trigger an action. In most situations, Udev operates behind the scenes. You don't have to be an expert in Udev to boot your computer or plug in a device, but if you feel like experimenting, you can configure Udev directly to automate an action. There's a good chance you are already familiar with starting and stopping systemd services by hand or enabling them to start at boot, but you can also have them start when certain ad hoc conditions are met. You could, for example, have systemd trigger an event when you plug in new hardware or when things change in the filesystem. You do that by combining a Udev rule with a systemd service.
This article shows how to leverage the kernel's Udev device manager and systemd's Device and Path units to create a home surveillance system with Single Board Computer (SBC) and an off-the-shelf webcam. The idea is that, when the SBC detects the camera has been connected (or when it detects the camera on boot), it will trigger a surveillance service that will take a picture every few seconds. If the surveillance script detects movement, it will save the images to a predetermined folder. These images will be saved with a unique date-and-time-based name.
I have several SBCs lying around from bygone eras, some never used and still in their original boxes. I picked a PINE 64A [1] (Figure 1), but any device that can run Linux will do. In my case, I'll use a version of Arch Linux that works well with the PINE 64A's ARMv8 architecture [2].
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