Ubuntu Debugging
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Boot Ubuntu without the graphical interface
It could be useful to boot our standard OMAP releases Ubuntu without the graphical environment, for example when you have an experimental kernel which limited graphics support, or when you just need to ssh on your system for native compiling (in which case the graphics would waste RAM and CPU).
To do this, you just need to add a parameter to the kernel bootargs. In the U-boot command line, just type:
setenv bootargs ${bootargs} text
boot
Of course, you could add saveenv to make this change permanent.
What's nice about this technique is that it doesn't require any change in the root filesystem.
Boot Ubuntu desktop / netbook on NFS
At least if you boot your root filesystem directly (without going through a standard Ubuntu initramfs), you probably noticed:
- that you can boot a minimal or server Ubuntu rootfs through NFS
- that you cannot boot a desktop type of Ubuntu rootfs (Ubuntu Desktop, Ubuntu Desktop Edition...)
The system hangs during the boot sequence. It's because of NetworkManager that reinitializes the network interface that you used for NFS.
A quick workaround is just to disable NetworkManager, for example by renaming the corresponding upstart configuration file:
sudo mv /etc/init/network-manager.conf /etc/init/network-manager.conf.disabled
Of course, this is shouldn't be done in a user environment, because users will need NetworkManager (to connect to their wired and wireless networks). However, this can make your life easier if you are involved in product test or development.
Debug the userspace init sequence
To trace the sequence of processes and events during the init sequence, you can run init in debug mode by adding init=/sbin/init --debug to the kernel command line. In the U-boot shell, for example:
setenv bootargs ${bootargs} init=/sbin/init --debug
This shows debug information in the system console.
