Debian/RHEL based Users

The nm-connection-editor is what you would normally use to auto-start a VPN on network connect. You would run nm-connection-editor in the terminal, select your network,

Go to the General tab, and turn on ‘Automatically connect to VPN’. Assuming you’ve set up your VPNs, this should be straight forward. And it is for Fedora and Ubuntu.

Arch Linux Users

UPDATE: This has been fixed as of 02/03/2021

Now the problem is that nm-connection-editor has been crashing on Arch Linux distros for months whenever you want to auto-start a VPN with a network connection.

https://forum.manjaro.org/t/cant-set-vpn-to-start-on-connection-nm-connection-editor-crashes/53689

Here is a temporary fix using the terminal, it assumes you have NetworkManager and have already setup the VPN.

First find the UUID of your VPN conneciton

Example

$ nmcli co

NAME                          UUID                                  TYPE  DEVICE
au-syd-udp                3e8e26ba-f7c0-4311-a657-cd9d4144d097  vpn   wlan0
Vulcan6                       0fe0d044-2fae-4a5a-816c-b2014715c9dd  wifi  wlan0

Then set the secondaries option of your wireless device to the UUID of the VPN. The connection.secondaries option determine secondary networks to start as the current network is started up. In this case, we want to start up au-syd-udp

In my case (Vulcan6 is an example)

$ nmcli co modify Vulcan6 connection.secondaries 3e8e26ba-f7c0-4311-a657-cd9d4144d097

Now restart your network connection, and it will autostart the VPN.

$ nmcli co down Vulcan6
$ nmcli co up Vulcan6

To reverse changes,

$ nmcli co modify Vulcan6 connection.secondaries ""

BE WARNED

nm-connection-editor will crash immediately when trying to edit the device with the secondaries option enabled in Arch Linux. If you want to edit without CLI, turn off the connection.secondaries and it will work again.

As I said, this is a temp fix, hope the GUI gets fixed soon.

To see all your options on the CLI

$ nmcli co show Vulcan6

See more at man nmcli-settings and man nmcli-examples