The serial console is a very helpful debugging tool for kernel development. However, when a crash occurs early in the boot process, one is left in the dark. There are two early console implementations available with different merits. This post will throw some lights on them.

earlyprintk

The kernel supports earlyprintk since… probably ever. At least 2.6.12, where the new age (git) started. After enabling “Kernel low-level debugging”, “Early printk” under “Kernel hacking” and selecting an appropriate low-level debugging port, you are ready to get early serial console output. Read more »