linux: added ip and wpa_supplicant

wiki/linux/ip.md

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+# IP
+
+`ip` is a program that can edit and display the configurations of network
+interfaces, routing and tunnels.
+It is a replacement for the program `ifconfig`.
+
+## List all network interfaces
+
+You can list network interfaces by running:
+
+```shell
+ip link list
+```
+
+## Enable/disable a network interface
+
+Assuming the interface is named `wlan0` run the following:
+
+```shell
+ip link set wlan0 up
+```
+
+Disabling works accordingly by running:
+
+```shell
+ip link set wlan0 down
+```

wiki/linux/wpa_supplicant.md

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+# WPA Supplicant
+
+`wpa_supplicant` is a free implementation of an IEEE 802.11i supplicant.
+It is especially interesting due to its WPA2 and WPA3 capabilities in contrast
+to other networking software.
+
+## Connect to a WPA2 secured WLAN
+
+This part assumes that your network interface is called `wlan0`
+(change it accordingly).
+
+- First make sure that your [network interface is up](./ip.md).
+- Save the authentication details to a file by running
+  `wpa_passphrase <SSID> >> /etc/wpa_supplicant.conf`
+- Connect to the WLAN by running
+  `wpa_supplicant -B -D wext -i wlan0 -c /etc/wpa_supplicant.conf`
+  (`-B` is optional for running the process in the background)