I have had some problems with kernels, modules, drivers, services, etc causing Centos to lock up when the system boots. This is real annoying when it has that nice fancy graphical grey screen up with the spinning device at the bottom, as you dont know what went wrong.
Now, when you boot, you can manually defeat that screen, but the next time you reboot, you have to go through the same process. I want to see what is going on all the time – every time. I like to see this, every time:
To get that to happen every time – even after you update the kernel, edit /etc/default/grub – you will find something like this:
GRUB_TIMEOUT=5 GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)" GRUB_DEFAULT=3 GRUB_DISABLE_SUBMENU=true GRUB_TERMINAL_OUTPUT="console" GRUB_CMDLINE_LINUX="rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet net.ifnames=0" GRUB_DISABLE_RECOVERY="true"
Mind you – yours might be slightly different – but what we are looking for is “rhgb quiet” in the GRUB_CMDLINE_LINUX. Remove those two words and save the file
Now, (as root) execute
grub2-mkconfig -o /boot/grub2/grub.cfg
and from now on, ever time you boot, you will see what is going on!