第 12 章 Getting started with kernel logging

During the boot process, the console provides important information about the initial phase of the system startup. To avoid loss of the early messages the kernel utilizes a ring buffer. This buffer stores all messages, including boot messages, generated by the printk() function within the kernel code. The messages from the kernel ring buffer are then read and stored in log files on permanent storage, for example, by the syslog service.

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.