linux: added wi-fi and troubleshooting

wiki/linux/networkmanager.md

@@ -2,6 +2,7 @@
 
 NetworkManager - short NM - is a program to automatically detect and connect to
 networks by providing options for various configuration.
+It is used to set up [Wi-Fi](/wiki/linux/wi-fi.md).
 
 ## Setup
 
@@ -26,3 +27,18 @@ This plugin can be installed with the `networkmanager-openvpn` package.
 OpenVPNs `.ovpn` files can then be imported by running
 `nmcli connection import type openvpn file <openvpn-file>`.
 Afterwards they can be modified accordingly.
+
+## Troubleshooting
+
+This section focusses on the troubleshooting of situations where the system does not connect
+correctly.
+
+### Restarting and Reenabling Wi-Fi
+
+A useful chain of commands is the following.
+It will restart the [SystemD](/wiki/linux/systemd.md) service and enable the Wi-Fi device.
+
+```sh
+systemctl restart NetworkManager
+nmcli radio wifi on
+```

wiki/linux/wi-fi.md

@@ -0,0 +1,27 @@
+# Wi-Fi
+
+Wi-Fi is a type of wireless network protocol that is used for local area networks.
+On [Linux-based systems](/wiki/linux.md) there are different programs that handle the Wi-Fi
+connection.
+
+- [WPA Supplicant](/wiki/linux/wpa_supplicant.md) is used for WPA2 and WPA3 connections among
+  others.
+- [NetworkManager](/wiki/linux/networkmanager.md) is used for various network connections.
+
+## Usage
+
+Tipps for usage can be found under the corresponding entries.
+
+## Troubleshooting
+
+Tipps for troubleshooting can be found under the corresponding entries, but the ones that use
+multiple programs to fix are listed here.
+
+### Restart WPA Supplicant and Reenable the Wi-Fi device
+
+A simple fix for many problems is a restart of [WPA Supplicant](/wiki/linux/wpa_supplicant.md)
+aswell as reenabling the Wi-Fi device using [NetworkManager](/wiki/linux/networkmanager.md).
+This can be done by first restarting WPA Supplicant as explained in the
+[corresponding section](/wiki/linux/wpa_supplicant.md#restarting-wpa-supplicant) and then
+reenabling the Wi-Fi device as explained in the
+[section of NetworkManagers entry](/wiki/linux/networkmanager.md#restarting-and-reenabling-wi-fi).

wiki/linux/wpa_supplicant.md

@@ -3,6 +3,7 @@
 `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.
+It is used to set up [Wi-Fi](/wiki/linux/wi-fi.md).
 
 ## Usage
 
@@ -17,3 +18,17 @@ This part assumes that your network interface is called `wlan0`
 - 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)
+
+## Troubleshooting
+
+This section focusses on the troubleshooting of situations where the system does not connect
+correctly.
+
+### Restarting WPA Supplicant
+
+Most of the problems regarding WPA Supplicant can be fixed by restarting the 
+[SystemD](/wiki/linux/systemd.md) service with the following command.
+
+```sh
+systemctl restart wpa_supplicant
+```