Bootloader - LILO or GRUB

Debian/Ubuntu uses GRUB.

• First GRUB finds HDD by its' UUID.
• Then OS kernel needs to see, where it is located on the HDD (by its UUID)
• Then additional tools are loaded to help OS boot (initrd). These tools are not used by the OS after boot (files are in /boot folder)

GRUB files can be edited in /boot/grub folder

Boot Logs + System Logs

dmesg command - changes, that take place in memory in boot process and after that as well

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messages file (/var/log/messages) - kernel info + application logs (like Apache) are stored here. This is the usual place to go for info in case of problems.

Init

Init - the very first process to boot in a kernel, in charge of all other processes.

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In some systems like UNIX only telinit command will be accepted. In those systems, init does not accept commands from a user, even a ROOT.

SHUTDOWN

shutdown -k - do not shutdown, just warn people

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