Printk ()

Links::

• http://janitor.kernelnewbies.org/docs/driver-howto.txt
• http://madwifi.org/wiki/DevDocs/KernelOops

Example::

printk( KERN_ERR "Failed to register device %s with major %d\n", MOD_NAME, MAJOR);

It is possible to read and modify the console loglevel using the text file

/proc/sys/kernel/printk.

The file hosts four integer values:

• current loglevel,
  
• default level for messages that lack an explicit loglevel,
  
• minimum allowed loglevel
• the boot-time default loglevel.
  

Writing a single value to this file changes the current loglevel to that value; thus, for example, you can cause all kernel messages to appear at the console by simply entering:

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

KERN_* parameters are defined in

include/linux/kernel.h

as follows:

Macro Name	Numeric Value	Description
KERN_EMERG	0	Used for emergency messages, usually those that precede a crash.
KERN_ALERT	1	A situation requiring immediate action.
KERN_CRIT	2	Critical conditions, often related to serious hardware or software failures.
KERN_ERR	3	Used to report error conditions; device drivers often use KERN_ERR to report hardware difficulties.
KERN_WARNING	4	Warnings about problematic situations that do not, in themselves, create serious problems with the system.
KERN_NOTICE	5	Situations that are normal, but still worthy of note. A number of security-related conditions are reported at this level.
KERN_INFO	6	Informational messages. Many drivers print information about the hardware they find at startup time at this level.
KERN_DEBUG	7	Used for debugging messages.