The following simple ant script fails on recent Linux systems (I have Ubuntu 11.10):

<?xml version="1.0" encoding="UTF-8"?>
<project name="langtools" default="get" basedir=".">
<target name="get">
<get src="http://download.java.net/jaxp/1.4.5/jaxp145_01.zip" dest="."/>
</target>
</project>


If you are behind a proxy, the get task will fail; a workaround used to be to set the -autoproxy option for ant, documented here:

http://ant.apache.org/manual/proxy.html

This option will have the effect of enabling the JVM propoerty 'java.net.useSystemProxies' which, will have the JDK to look at common system-wide settings for the proxy setup. It appears the JDK is not able to look at the newer gnome3 settings which are becoming the default on modern linux platoforms.

The result is that the system proxy settings are ignored - this bug is somewhat similar to oher bugs affecting other applications who used to fetch system-wide Gnome2 data:

https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/875266