reFind boot options does not show after installation of Ubuntu 16.04 Server LTS My Base OS is Sierra 10.12.5
Model MacBook Pro Mid-2014 Model
Model ID: 11,3

I have encountered an issue with reFind after installing Ubuntu server 16.04 LTS.  It seems that the boot options doesn't appear anymore and it automatically boots the Ubuntu OS.  The only way I can go back to my base OS is pressing the ALT key after rebooting it and before the chime sounds.  Anybody knows what I need to do with reFind or what commands to issue on the MacOS terminal in order to show the reFind boot options again?

Thanks,
So the designer of reFind was kind enough to respond to me and pointed out that the issue I am facing is a boot coup
http://www.rodsbooks.com/refind/bootcoup.html
Re-installing reFind did the trick.

Thanks Rod!!!