Skip to content

Use Px as Local Proxy on a Windows Host

This documentation is for Windows hosts only without direct internet access.


Host computers without direct internet access are using a proxy server to connect to the internet. In this case we have to provide the proxy service also for a SDK builder VM running on this host.

We recommend to install and run px.exe as local proxy server on your Windows host. This local proxy forwards http and https requests to the configured remote proxy.

Here some advantages of px.exe:

  • Simple to install and configure
  • Same port for http and https forwarding
  • No need to store credential informations (user, password) in config file(s) because Px uses the encrypted Windows credentials.
  • Preconfigured usage in the ctrlX AUTOMATION SDK QEMU VMs

For more informations about Px see What is Px

Installation of Px as Local Proxy Server

  • Open
  • Click button Latest
  • Click px-v?.?.? (v?.?.? e.g. v0.8.4)
  • The zip archive will be downloaded
  • Unzip the content e.g. to c:\tools\px
  • Create a px-start.bat file in with the content:

    cd c:\tools\px


  • Manually call this bat file

Enter this command for further usage of Px:

px.exe --help

For automatically run at startup do following steps:

  • Create a link to px-start.bat
  • Open the startup folder with Windows logo key + R, enter shell:startup
  • Move the link to px-start.bat into this folder


Px provides both http and https access via default port 3128. If this port is not available on the host it can be changed in px.ini BUT: The alternative port has to be changed in the VM too - see Setup a QEMU VM and Setup a Virtual Box VM.

Proxy Settings in the App Build Environment

As mentioned a VM running on a host without direct internet access has to use a proxy server too.

For the VM Px on the host is reachable via the URL

Note: is the IP address of the host from the perspective of the App Build Environment. See also QEMU Virtual Machine Networking

For your information only - do not change if not necessary:

This URL is stored as so called "Proxy Settings" in the VM e.g. in following files:

  • /etc/environment *1)
  • /etc/wgetrc
  • ~/.nuget/NuGet/NuGet.Config

*1) Here these environment variables are defined:

  • http_proxy=""
  • https_proxy=""
  • no_proxy=localhost,,.local


Check proxy function in the App Build Environment:


If no error occurs the internet access via the proxy server is working. In this case remove the downloaded file.

rm index.html*

Check the following points if there are problems with Px:

  • Are the proxy settings Proxy Settings in the App Build Environment fitting to the px.ini file on the host?
  • For more informations about the settings in see px.ini on github
  • Host PC: Is another proxy running e.g. cntlm?
  • Host PC: Enable logging with parameter log = 1 in px.ini