Debugging with printk

• Universal debugging technique used since the beginning of programming (first found in cavemen drawings)

• Printed or not in the console according to the priority. This is controlled by the loglevel kernel parameter, or through /proc/sys/kernel/printk (see Documentation/sysctl/kernel.txt)

• Available priorities (include/linux/kernel.h):

#define KERN_EMERG "<0>" /* system is unusable */ #define KERN_ALERT "<1>" /* action must be taken immediately */ #define KERN_CRIT "<2>" /* critical conditions */ #define KERN_ERR "<3>" /* error conditions */ #define KERN_WARNING "<4>" /* warning conditions */ #define KERN_NOTICE "<5>" /* normal but significant condition */ #define KERN_INFO "<6>" /* informational */ #define KERN_DEBUG "<7>" /* debug-level messages */