Error running spring-boot-admin-sample [clean]: No valid Maven installation found. Either set the home directory in the configuration dialog or set the M2_HOME environment variable on your system.

You can encounter the following error in IntelliJ on Mac:

Error running spring-boot-admin-sample [clean]: No valid Maven installation found. Either set the home directory in the configuration dialog or set the M2_HOME environment variable on your system.

Setting M2_HOME doesn't work.

You'd better set your Maven home directory in IntelliJ as follows:

Preferences -> Maven -> Maven home directory

Reference:
http://stackoverflow.com/questions/7053666/maven-home-m2-home-not-being-picked-up-by-intellij-idea