Where to find ubuntu boot logs?

Question

My Xubuntu 14.04 installation stopped booting all of a sudden: after rebooting I just see a flashing _ in the top left corner of the screen. Holding Left-Shift during boot won't open any menu, Ctrl+Alt+F* will not open a terminal I can type in.

I've reset BIOS settings, which did not help, then made a bootable USB stick with Ubuntu. I can now boot and I see that the data on the disk with OS is intact, I've checked the disk with badblocks and it found no errors.

Is there any way I can locate any details as to why the system does not boot?

Solution

You can use two log files to view the boot problem.

/var/log/boot.log  ---  System boot log

/var/log/dmesg     ---  print or control the kernel ring buffer

Just use dmesg in terminal to view event occurred since boot.

Comments

[laugh salutes Monica C]

With Ubuntu 15.4 onward this won't work anymore (or will give you an old boot log from a prior version). See askubuntu.com/a/821801/206303 for an updated answer.