The start up process executes some commands, if the command returns a 0 status -executed- the green OK will print on the screen during boot. If it returns other value status, a red FAILED will be printed.

results of these success and fail will also be logged into the system log, including error messages so you can correct the missing service(s). You can then view last entries 10 in this file by

tail /var/log/messages 

or

 tail -nXX /var/log/messages 

where XX is nom. of lines.

And this makes gnu/Linux have more reliability than other OSs.

Diaa Radwan.