Some useful links to explain the concepts of the Boot Process
- https://www.ibm.com/developerworks/library/l-linuxboot/
- https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-1.html
- http://www.slashroot.in/linux-booting-process-step-step-tutorial-understanding-linux-boot-sequence
- http://www.golinuxhub.com/2014/03/step-by-step-linux-boot-process.html?
- http://www.tecmint.com/linux-boot-process/
- https://www.digitalocean.com/community/tutorials/the-upstart-event-system-what-it-is-and-how-to-use-it
- http://linoxide.com/booting/boot-process-of-linux-in-detail/
- http://bencane.com/2013/09/16/understanding-a-little-more-about-etcprofile-and-etcbashrc/
- http://www.if-not-true-then-false.com/2012/delete-remove-old-kernels-on-fedora-centos-red-hat-rhel/
- https://linuxconfig.org/how-to-remove-unused-kernel-images-from-centos-linux-system
- https://markmcb.com/2013/02/04/cleanup-unused-linux-kernels-in-ubuntu/
- http://www.ostechnix.com/how-to-create-bootable-usb-drive-using-dd-command/
- https://blog.packagecloud.io/eng/2016/03/08/how-to-extract-and-disassmble-a-linux-kernel-image-vmlinuz/