To execute a process, the user needs to have execute permission for the executable file. To access any executable file ( and in fact, any file ), the user ID must have directory search permission for the folder ( directory ) in which the file resides.

Please note that UNIX ( or any multi-tasking operating system like Linux or Android or Windows ) is a very complex operating system with lot of sub-systems needed to perform the tasks. Hence it is almost impossible to understand the inner working details of individual sub-subsystems completely by listening to one session. You would need to complete a few more sessions of the specific topic and probably repeat all the sessions of the topic before you can completely comprehend a part of the UNIX system in its entirety. You may have to listen to sessions of other parts of the system also because the sub-systems are inter-dependant. Process Management system has dependencies on File Management system and vice versa. Hence one round of completing all sessions is to be followed by repeating select topics. This is what thousands of earlier students have done. You have the added disadvantage of writing and testing of C programs on your own. It pays to repeat C programming sessions several times before you get the critical mass of understanding that can explode to full understanding.

Best Wishes,

MLS Shastry