Added opensuse's notes to the knowledge base

knowledge base/opensuse linux.md

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+# OpenSUSE
+
+## Enable Bluetooth pairing on boot
+
+1. enable the `bluetooth` service on boot
+1. install `bluez-auto-enable-devices`; this will create the configuration file `/etc/bluetooth/main.conf`
+
+Also see specific settings in the [Bluetooth] KB.
+
+## Enable SSH access from outside after installation
+
+Open port 22 on the firewall:
+
+- using Yast:
+
+  1. open _Yast2_ > _Firewall_
+  1. make sure your interfaces are appointed to the _External_ zone
+  1. check _ssh_ is in the _Allowed services_ column and add it to the list if not
+  1. save the configuration and exit (make sure the firewall is reloaded on exit)
+
+- using [firewall-cmd][firewalld] on the command line:
+
+  ```shell
+  sudo firewall-cmd --add-port=22/tcp --permanent
+  ```
+
+Start the SSH daemon:
+
+- using Yast: open _Yast2_ > _System services_ and enable _SSHD_
+- using [systemctl][systemd] on the command line:
+
+  ```shell
+  sudo systemctl enable --now sshd.service
+  ```
+
+## Raspberry Pi
+
+Install the OS from another computer capable of reading and writing SD cards.
+
+Given `/dev/sdb` being a SD card, use the following:
+
+```shell
+curl -C - -L -o opensuse.raw.xz http://download.opensuse.org/ports/aarch64/tumbleweed/appliances/openSUSE-Tumbleweed-ARM-JeOS-raspberrypi.aarch64.raw.xz
+xzcat opensuse.raw.xz \
+ | sudo dd bs=4M of=/dev/sdb iflag=fullblock oflag=direct status=progress \
+ && sync
+```
+
+Insert the SD card in the Raspberry Pi and power it on. The network is configured to get an IP address on `eth0` using DHCP.
+
+Connect using SSH and login using `root:linux`.
+
+### Firmware update from a running system
+
+```shell
+# Check for an updated firmware.
+sudo rpi-eeprom-update
+
+# Install the new version and reboot.
+sudo rpi-eeprom-update -a && sync && reboot
+```
+
+## Further readings
+
+- [Bluetooth]
+- [Firewalld]
+- [Systemd]
+
+## Sources
+
+- [OpenSSH basics]
+- [Bluetooth on boot]
+- [Raspberry Pi4]
+
+<!-- further readings -->
+
+[bluetooth]: bluetooth.md#bluetooth-devices-cannot-be-used-at-login
+[firewalld]: firewalld.md
+[systemd]: systemd.md
+
+[bluetooth on boot]: https://www.reddit.com/r/openSUSE/comments/eoozm2/comment/feetqpn/
+[openssh basics]: https://en.opensuse.org/SDB:OpenSSH_basics
+[raspberry pi4]: https://en.opensuse.org/openSUSE:Raspberry_Pi