Can you help me setup proxy chaining properly on Linux/Ubuntu, please ?

I work in a remote location and I am connected to my company by a proxy tunnel. It works on port 3128 and is setup system wide (Gnome Settings > Network > Manual proxy)

The way I understand it, I should setup my browser (in its own proxy settings) to listen on the port 8866 (e.g. Fiddler), then Fiddler should be setup to listen through the system proxy.

The problem is when I start capturing traffic, Fiddler replaces my system wide proxy settings by its own (port 8886), and revert back to my previous settings when I stop capturing. But I would not want Fiddler to touch the proxy system settings at all, would I ? It seems to me that Fiddler changing the Gnome system settings prevents proxy chaining.

In Fiddler:

Connection

- port: 8886

- Act as system proxy on startup: Unchecked

Gateway

- Use system proxy (recommended): Selected

Hey,

Thank you for sharing the details of your setup. Let me try to explain how Fiddler Everywhere works with the predefined proxy and suggest an approach how to handle your case.
By default, once you sign in, Fiddler Everywhere will act as system proxy and will work with your OS proxy settings. However, before replacing the OS proxy settings, Fiddler Everywhere reads the current settings and persists them. After that Fiddler Everywhere will set your OS System Proxy to point to its own proxy server. However, each request that is captured by Fiddler Everywhere will be sent from Fiddler's Proxy server to your previously set proxy server. So the proxy chaining should happen out of the box.
Of course, the applications must respect the OS proxy settings (especially when they are changed by Fiddler Everywhere). If that's not the case, you have to manually set the application's proxy configuration to point to Fiddler Everywhere's proxy. As already explained, each request will be automatically sent to your proxy that was set prior starting Fiddler.

Of course, there's another way to do this - instead of reading the proxy settings from the OS, you can also use the Settings -> Gateway configuration and select Manual Proxy configuration. There you can enter the config of your proxy. This way, after you sign in, Fiddler will direct all captured requests to this particular proxy.

So can you try doing the following:
1. Ensure Fiddler Everywhere is stopped.
2. Ensure your proxy configuration se set.
3. Start Fiddler Everywhere and sign in.
4. Start capturing.
5. Check if requests from your browser are successfully captured by Fiddler Everywhere and if they are successful (you'll have to trust the root certificate before that and enable capturing of HTTPS traffic).

Hope this makes it more clear how the proxy chaining should work. If it does not work on your side, please share more details about your setup and the actual errors that you see in your browser or in the app.

Regards,
Rosen