What happens before you can log in.
WHY IT MATTERS
When a machine does not come back, knowing the sequence tells you where it stopped.
WHAT THE STAGES ARE
Firmware initialises hardware A boot loader is found and run The boot loader loads a kernel The kernel mounts the root file system The init system starts services Login becomes available
WHAT THE BOOT LOADER DOES
Offers a choice of kernels and passes options to the one chosen.
WHY THAT CHOICE MATTERS
A machine failing on a new kernel can be booted on the previous one.
WHAT FAILS AT THE FILE SYSTEM STAGE
An entry in the file system table referencing something absent.
WHAT THAT PRODUCES
A machine dropping to an emergency prompt rather than booting.
WHY IT IS A COMMON CAUSE
Storage was removed or renamed, and the table was not updated.
WHAT TO DO ABOUT IT
Boot to rescue, correct the table, and reboot.
WHAT FAILS AT THE SERVICE STAGE
A service configured to start that cannot.
WHY THAT IS USUALLY SURVIVABLE
The machine still boots, and the service reports why.
HOW TO SEE WHAT HAPPENED DURING BOOT
The journal, restricted to the last boot.
WHAT TO CHECK AFTER ANY REBOOT
That every expected service started, rather than assuming.
WHAT TO ARRANGE BEFORE REBOOTING ANYTHING REMOTE
Console access.
