There are eight possible loglevel strings, defined in the header <linux/kern_levels.h> :

#define KERN_SOH "\001"  /* ASCII Start Of Header */
#define KERN_SOH_ASCII '\001'

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

#define KERN_DEFAULT KERN_SOH "d" /* the default kernel loglevel */