If you uninstall Java, or it is installed in a way that the solr service can’t see, you can get the following error:
The currently defined JAVA_HOME (/usr/lib/jvm/java-8-oracle) refers to a location where Java could not be found. Aborting. Either fix the JAVA_HOME variable or remove it from the environment so that the system PATH will be searched.
To fix this, you can edit /etc/default/solr.in.sh, and add the following line (adjust to match your JDK):
SOLR_JAVA_HOME="/usr/lib/jvm/java-7-openjdk-i386"