Cross-platform Profile Activiation: Is Example 11.4 Correct?

Example 11.4: Problems with including OS check and file exists check. I am trying to check for linux and a file exists. If on windows the profile does not trigger. On linux the profile always executes. I took out the os check and then the file exists check worked. So I do not know what I am doing wrong.

<profiles>
<profile>
<id>linux</id>
<activation>
<activebydefault>false</activebydefault>
<os>
<family>unix</family>
</os>
<file>
<exists>src/main/rpm/release.xml</exists>
</file>
</activation>
<build>
<plugins>
<plugin>
<groupid>org.apache.maven.plugins</groupid>
<artifactid>maven-antrun-plugin</artifactid>
<version>1.2</version>
<executions>
<execution>
<phase>deploy</phase>
<configuration>
<tasks>
<ant target="release">
<property name="release.version" value="${project.version}">
</property></ant>
</tasks>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</profile>
</profiles>