Linux kernel provides around 8 log levels to identify / distinguish the kernel messages or logs.
KERN_EMERG:
Used for emergency messages, usually those that precede a crash.
KERN_ALERT:
A situation requiring immediate action.
KERN_CRIT:
Critical conditions, often related to serious hardware or software failures.
KERN_ERR:
Used to report error conditions; device drivers often use KERN_ERR to report hardware difficulties.
KERN_WARNING:
Warnings about problematic situations that do not, in themselves, create serious problems with the system.
KERN_NOTICE:
Situations that are normal, but still worthy of note. A number of security-related conditions are reported at this level.
KERN_INFO:
Informational messages. Many drivers print information about the hardware they find at startup time at this level.
KERN_DEBUG: