The kernel uses a ring buffer to store printk() messages, preserving critical information during system startup. This preserves early boot messages before services such as syslog can read and save them to permanent storage.

The ring buffer is a cyclic data structure that has a fixed size, and is hard-coded into the kernel. Users can display data stored in the kernel ring buffer through the dmesg command or the /var/log/boot.log file. When the ring buffer is full, the new data overwrites the old.

See syslog(2) and dmesg(1) man pages on your system for more information.