v4l2 and obs: added

wiki/linux/systemd.md

@@ -28,3 +28,15 @@ initializing.
 ```txt
 After=pve-guests.service
 ```
+
+Such a service can be started by running:
+
+```sh
+sudo systemctl start unturned
+```
+
+Alternatively it can be enabled to start at every boot by running:
+
+```sh
+sudo systemctl enable unturned
+```

wiki/linux/v4l2.md

@@ -0,0 +1,54 @@
+# V4L2
+
+V4L2 is the second version of
+[Video4Linux](https://www.linuxtv.org/wiki/index.php/Main_Page).
+It functions as a driver for webcams and tv tuner cards and other devices.
+
+## v4l2loopback
+
+The following section is based on a
+[gist by ioquatix](https://gist.github.com/ioquatix/18720c80a7f7eb997c19eef8afd6901e).
+
+To use [v4l2loopback](https://github.com/umlaeute/v4l2loopback) an according
+package needs to be installed.
+Some distributions have a package named `v4l2loopback-dkms` in the package
+manager, making the manual installation process unnecessary.
+Afterwards v4l2loopback can be manually started by running:
+
+```sh
+modprobe v4l2loopback card_label='V4L2 Loopback' video_nr=7 exclusive_caps=1
+```
+
+`video_nr=7` states the device path to use with v4l2loopback - in this case
+`/dev/video7`.
+This can be changed according to the needs.
+It is important that the device is not already in use by another application.
+
+For an automatic start at boot via [SystemD](./systemd.md) a service can be
+created - as described in [the SystemD entry](./systemd.md#run-command-on-boot).
+For v4l2loopback create the file `/etc/systemd/system/v4l2loopback.service`
+containing the following lines:
+
+```txt
+[Unit]
+Description=V4L2 Loopback
+
+[Service]
+Type=simple
+RemainAfterExit=yes
+ExecStart=/bin/modprobe v4l2loopback card_label='V4L2 Loopback' video_nr=7 exclusive_caps=1
+ExecStop=/bin/rmmod v4l2loopback
+
+[Install]
+WantedBy=default.target
+```
+
+Note the line starting with `ExecStart=/bin/` is the same line described above
+to change the device path.
+Make sure to change it if needed.
+
+Afterwards enable the service to start at every boot process by running:
+
+```sh
+sudo systemctl enable v4l2loopback
+```