I am using Ubuntu 12.04 at work and we have a proxy server. I would like to allow guests to use my computer on the guest account, but I cannot get the proxy settings to stay. Is there a way to set the proxy setting automatically at log-in for the guest account? The AskUbuntu question Change default guest session launcher applications? shows how to configure the launcher icons. Can I use this file to set a persistent proxy server setting? If so, how?
Most likely you can use the same approach as in the other question, provided that you figure out what the command is. In 12.04 I think it would be
However, if you go to System Settings -> Network -> Network proxy, there is an "Apply system wide" button (at least in 13.04). Making the proxy settings system wide is possibly a simpler way to achieve what you want.
Another possibility: I wrote a tutorial about guest session customization. The tutorial was originally published at Ubuntu Forums, and there a user added a step-by-step guide showing an alternative method to customize guest sessions.