Finding the root directory of a multi module maven reactor project

use ${session.executionRootDirectory}

For the record, ${session.executionRootDirectory} works for me in pom files in Maven 3.0.3. That property will be the directory you're running in, so run the parent project and each module can get the path to that root directory.

I put the plugin configuration that uses this property in the parent pom so that it's inherited. I use it in a profile that I only select when I know that I'm going to run Maven on the parent project. This way, it's less likely that I'll use this variable in an undesired way when I run Maven on a child project (because then the variable would not be the path to the parent).

For example,

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <executions>
        <execution>
            <id>copy-artifact</id>
            <phase>package</phase>
            <goals>
                <goal>copy</goal>
            </goals>
            <configuration>
                <artifactItems>
                    <artifactItem>
                        <groupId>${project.groupId}</groupId>
                        <artifactId>${project.artifactId}</artifactId>
                        <version>${project.version}</version>
                        <type>${project.packaging}</type>
                    </artifactItem>
                </artifactItems>
                <outputDirectory>${session.executionRootDirectory}/target/</outputDirectory>
            </configuration>
        </execution>
    </executions>
</plugin>

Something which I have used in my projects is to override the property in the sub-module poms.

    root:           <myproject.root>${basedir}</myproject.root>
    moduleA:        <myproject.root>${basedir}/..</myproject.root>
    other/moduleX:  <myproject.root>${basedir}/../..</myproject.root>

This way you still have the relative paths, but you can define a plugin once in the root module, and your modules will inherit it with the right substitution for myproject.root.

Since Maven 3.3.1, you can use ${maven.multiModuleProjectDirectory} for this purpose. (thanks to https://stackoverflow.com/a/48879554/302789)

edit: this seems to only work properly when you have a .mvn folder at the root of your project.