Wifi disconnects randomly after several hours (18.04)

This is often the result of the power saving feature in Ubuntu. You can disable this for the WiFi device by editing a file and restarting the network manager.

Here's how:

0. Open Terminal (if it's not already open)

1. Edit the default-wifi-powersave-on.conf file:

   sudo vi /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
   

   ^{Note: Feel free to use any text editor of your choice. Be sure to open it with sudo, though.}

   You will see the file contents look like this:

   [connection]
   wifi.powersave = 3
   

2. Replace 3 with 2, then save the file.

   Definition of Values:

   Value	What It Means
   0	Use the default value
   1	Do not change existing setting(s)
   2	Disable powersave feature
   3	Enable powersave feature

3. Restart the network manager:

   sudo service network-manager restart
   

   ^{Alternatively, you could restart the entire system.}

This should prevent the device from disconnecting from the network when the system believes it is idle.