Issues with <exec> ANT task

The exec ant task is used to execute a system command. I came across the syntax that works on Windows but does not work on Linux.

Works on Windows:

<exec executable="${ant.home}/bin/ant" failonerror="true"
dir="${sandbox.path}/${processName}">
<arg value="-Dhttp.hostname"/>
<arg value="-Dhttp.hostname=${http.host}"/>
<arg value="-buildfile= build.xml"/>
</exec>

The tweak to make it working on the Linux,

<exec executable="${ant.home}/bin/ant" failonerror="true"
dir="${sandbox.path}/${processName}">
<arg value="-Dhttp.hostname"/>
<arg value="-Dhttp.hostname=${http.host}"/>
<arg value="-buildfile"/>
<arg value="build.xml"/>
</exec>