Kernel debugging

Name	String	Meaning	alias function
KERN_EMERG	"<0>"	Emergency messages, system is about to crash or is unstable	pr_emerg
KERN_ALERT	"<1>"	Something bad happened and action must be taken immediately	pr_alert
KERN_CRIT	"<2>"	A critical condition occurred like a serious hardware/software failure	pr_crit
KERN_ERR	"<3>"	An error condition, often used by drivers to indicate difficulties with the hardware	pr_err
KERN_WARNING	"<4>"	A warning, meaning nothing serious by itself but might indicate problems	pr_warning
KERN_NOTICE	"<5>"	Nothing serious, but notably nevertheless. Often used to report security events.	pr_notice
KERN_INFO	"<6>"	Informational message e.g. startup information at driver initialization	pr_info
KERN_DEBUG	"<7>"	Debug messages	pr_debug, pr_devel if DEBUG is defined
KERN_CONT	"<c>"	"continued" line of log printout (only done after a line that had no enclosing \n) [1]	pr_cont

현재 log level

$ cat /proc/sys/kernel/printk
	7       4       1       7
	current	default	minimum	boot-time-default

Log Level 수정

# echo 8 > /proc/sys/kernel/printk

pr_debug()

    Some files call pr_debug(), which is ordinarily an empty macro that discards
    its arguments at compile time.  To enable debugging output, build the
    appropriate file with -DDEBUG by adding

      CFLAGS_[filename].o := -DDEBUG

    to the makefile.

    For example, to see all attempts to spawn a usermode helper (such as
    /sbin/hotplug), add to lib/Makefile the line:

        CFLAGS_kobject_uevent.o := -DDEBUG

    Then boot the new kernel, do something that spawns a usermode helper, and
    use the "dmesg" command to view the pr_debug() output.