Ubuntu 20.04 LTS and newer

With GNOME 3.36 desktop on Ubuntu 20.04 LTS, WiFi tethering has become easier than ever!? Just open the Wi-Fi Settings from system menu.

In the Wi-Fi Settings window, click on the drop-down menu on top right and select Turn On Wi-Fi Hotspot option.

A dialog will show up, where you can set the name and password for your new hotspot.

If your hotspot gets created successfully, Wi-Fi Settings would now show a section with a toggle for the newly created hotspot.

A hotspot indicator would appear on the top bar as well, showing it's active status.

If you need to edit the hotspot and do more advanced configuration, follow instructions similar to that of Ubuntu 18.04 LTS described below.

Ubuntu 18.04 LTS

GNOME 3.28 desktop on Ubuntu 18.04 LTS makes it easy to start a WiFi hotspot. Open the Wi-Fi Settings from system menu.

And then from the hamburger menu on Wi-Fi Settings, select Turn On Wi-Fi Hotspot. That's it, your WiFi access point is now up and running!

Advanced Stuff

If you wanna change the name (SSID) and password of your access point, open Network Connections editor tool by entering the following in either Terminal or Alt+F2:

nm-connection-editor

Double click on Hotspot and the editor window'll appear. You may change SSID and password from the Wi-Fi and Wi-Fi Security tabs.

Ubuntu 16.04 LTS & 14.04 LTS

Step 1: Test whether your WiFi card supports AP mode

Follow the Access Point mode check in the answer provided by Web-E

Step 2: Start the built-in Hotspot

Network comes with a built-in option to start an Ad-Hoc hotspot. So, let's use this first, so that it could be configured and converted to an Access Point mode hotspot in the next step.

Search Network in Dash and open it.

Press the "Use as Hotspot" button and Network Manager will start an AdHoc hotspot.

But that's not what we want, is it? ? Stop the hotspot.

Step 3: Configure Hotspot

Open Network Connections from Dash or 'Edit Connections' from Network Indicator menu.

In the Network Connections window that appears, there'll be a connection named Hotspot listed under the WiFi section. Select it and click the 'Edit' button.

In the window that appears, you may edit the broadcast name (SSID) of your hotspot. Now comes the most important part of this configuration: change mode to 'Hotspot', which'll finally convert the hotspot to Access Point mode. Users of Ubuntu 14.04 LTS'll notice that this mode isn't available to choose from the dropdown. Don't get disappointed, as you can still do it via an extra Step 3.1.

Save and open the same Editing Hotspot window again. This time go to the WiFi Security tab for selecting password type. If you don't want to set a password, you can set security to none and thus create an open hotspot. If you're setting a password, it's recommended to change the security key from WEP to WPA2. Once the configurations are done, don't forget to save it so that the changes could apply.

In the General tab, make sure that “Automatically connect to this network when it is available” is turned off (unless you only ever use your wifi as a hotspot). Otherwise, since the hotspot is always available, you won't see the menu entries to connect to other wifi networks in the network manager applet.

Step 3.1: Only for Ubuntu 14.04 LTS

Since Ubuntu 14.04 LTS's Networks (network-manager v9.8.8) doesn't offer a graphical setting to select AP mode, we'll manually edit it's config file to force the conversion. Copy the following command, then press Alt+F2 or open Terminal and paste it there:

pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY gedit /etc/NetworkManager/system-connections/Hotspot

Type your password in the authorization dialog that appears and the configuration file will be opened in text editor. Find a line beginning with mode=, change it to mode=ap and save the file.

Step 4: Start Hotspot

Now that the configuration part is over, we'll start the hotspot. Click on 'Create New Wi-Fi Network' from Network Indicator menu.

In the window that appears, click on the connection drop-down button and change "New..." to "Hotspot". Press the "Create" button and your hotspot will start running. From now on, whenever you need a hotspot, you just need to do this step i.e Step 4 only.

K.. That's all folks! Have fun with your new Access Point ?

Switching to an open source driver did it

Short Version

Using an open source driver (brcmsmac in my case) instead of the Proprietary Broadcom STA Wireless driver (wl) and installing ap-hotspot did the trick

Long version for Broadcom Users

1. Go to Ubuntu Broadcomm WifiDocs. See if an open source alternative exists.

2. The Linux drivers page should tell you if it supports AP mode

   • If so yay!
   • If not, I can't help. Sorry.

3. Temporarily switch to the open- driver source to check if it does what you want

   #unload all drivers
   sudo modprobe -r b43 bcma
   sudo modprobe -r brcmsmac bcma
   sudo modprobe -r wl
   
   #load the corresponding open-source driver (brcmsmac in my case)
   sudo modprobe brcmsmac
   

   If it works, you can edit the blacklists to make sure only the required driver works. An easier option would be to simply uninstall the proprietary drivers using sudo apt-get purge bcmwl-kernel-source

4. Install ap-hotspot. Remember, there are some issues in 14.04, and rolling back must be done as shown in the page. Else, use hostapd as described here

5. Run sudo ap-hotspot start. Your android phone should work with this conection.

6. Open source wins again