Issue
The catalina.out file grows to a potentially large size with pairs of WARNINGs every 30 seconds like the following:
Dec 30, 2019 7:22:39 PM java.util.prefs.FileSystemPreferences checkLockFile0ErrorCode
WARNING: Could not lock User prefs. Unix error code 2.
Dec 30, 2019 7:22:39 PM java.util.prefs.FileSystemPreferences syncWorld
WARNING: Couldn't flush user prefs: java.util.prefs.BackingStoreException: Couldn't get file lock.
Dec 30, 2019 7:23:09 PM java.util.prefs.FileSystemPreferences checkLockFile0ErrorCode
WARNING: Could not lock User prefs. Unix error code 2.
Dec 30, 2019 7:23:09 PM java.util.prefs.FileSystemPreferences syncWorld
WARNING: Couldn't flush user prefs: java.util.prefs.BackingStoreException: Couldn't get file lock.
Dec 30, 2019 7:23:39 PM java.util.prefs.FileSystemPreferences checkLockFile0ErrorCode
WARNING: Could not lock User prefs. Unix error code 2.
Dec 30, 2019 7:23:39 PM java.util.prefs.FileSystemPreferences syncWorld
WARNING: Couldn't flush user prefs: java.util.prefs.BackingStoreException: Couldn't get file lock.
Cause
The Tomcat application server (which the Contrast EOP installation uses to serve up its UI) expects a home folder to exist belonging to the user account under which it is running, in order to store the Java system preferences file.
Resolution
Create the missing home folder /home/contrast_service containing a .java/.systemPrefs subfolder - making sure the owner and group of these is contrast_service and then restart contrast-server.