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How to fix Linux boot problems

Mar 03, 2009, 18:03 (0 Talkback[s])

"Grokking the problem
When I'm teaching Linux on one of my courses, many attendees tell me they are interested in troubleshooting of one form or another. Some of them are looking for a cookbook approach - "If you see the error message X, run command Y", but troubleshooting rarely works that way. My initial advice to anyone who needs to troubleshoot is always the same: "The most important thing in troubleshooting is to understand how the system is supposed to work in the first place. The second most important thing is figuring out exactly what the system was trying to do when it went wrong."

"With this in mind, let's take a look at how Linux boots. Knowing the normal sequence of events, and determining how far it got before it ran into trouble, are key to diagnosing and fixing boot-time problems. Figure 1 above, right shows the normal sequence of events (green arrows) and indicates some of the possible failure paths (red arrows).

"Picking yourself up by your bootstraps
Booting is a multi-stage affair. When a PC is powered up, control initially passes to a program (called the BIOS) stored in read-only memory on the motherboard. The BIOS performs a self-test of the hardware and scouts around looking for a device to boot from. The BIOS provides configuration screens that allow you to assign the order in which it searches for a bootable device, and modern BIOSes support a wide range of boot devices, including PXE booting from a network server. The only case we consider here is booting from the hard drive."

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