Debugging casper (booting the live CD)

casper and kernel log files

For debugging casper please boot with the boot option (e.g. kernel line in grub or append line in isolinux) “debug=”. At the live CD boot menu, press F6 and add debug= to the list of parameters:

append  file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.gz debug=

Removing quiet and splash is generally a good idea when debugging.


The debug log file is /casper.log inside the initrd temporary filesystem, but will be copied to /var/log/casper.log in the fully booted system. The kernel log will be in /var/log/dmesg.log. If the system does not boot up, retrieving the log files for attaching to the bug report can be an exercise of its own:

  1. plug in an usb stick
  2. watch the kernel messages and look for the partition on the stick, for instance /dev/sdb1
  3. or check with ls /dev/sd* if you can recognize it
  4. mkdir /tmp/stick
  5. mount /dev/sdb1 /tmp/stick
  6. cp /casper.log /tmp/stick/
  7. dmesg > /tmp/stick/dmesg.txt
  8. umount /tmp/stick
  9. unplug the stick and give us the files casper.log and dmesg.txt!

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