You are on this page means, there is not much information on Error ID - c51399ee on google. Hope this post on how to solve phusion passenger preloader error might save your day. Well the LoadError comes from a failure by Ruby to load the phusion passenger.so module.   The Secret of Error ID: c51399ee I am using - ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [aarch64-linux] , this issue appears on ARM - aarch64 based system and it works well with ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux-gnu]. You can check apache error log from your /var/log/apach2 directory. $ tail -100 /var/log/apache2/error.log App 2001 stderr: /usr/bin/passenger-config:27:in `require': cannot load such file -- phusion_passenger (LoadError) App 2001 stderr: