You may see an exception similar to this:

StandardManager[/confluence]: IOException while loading persisted sessions: java.io.WriteAbortedException: writing aborted;
java.io.NotSerializableException: bucket.search.lucene.SearchWordsLister
java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: bucket.search.lucene.SearchWordsLister
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1278)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1845)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1769)

This is because Confluence's HTTP sessions may contain objects which cannot be serialized to disk. Tomcat tries to serialize existing sessions by default during shutdown.

You can add the following configuration parameter into Tomcat's server.xml file between the <Context> tags to disable this:

<Manager className="org.apache.catalina.session.PersistentManager" saveOnRestart="false"/>

Related topic

For more information regarding the saveOnRestart parameter, please refer to the Server Configuration Reference for the Manager Component