[sri@localhost ~]$ sudo cat /proc/sys/kernel/printk
4   4   1   7

dmesg -n 3

[sri@localhost ~]$ sudo bash -c 'echo 3 > /proc/sys/kernel/printk'
[sri@localhost ~]$ sudo cat /proc/sys/kernel/printk
3   4   1   7

printk(KERN_EMERG   "KERN_EMERG");
printk(KERN_ALERT   "KERN_ALERT");
printk(KERN_CRIT    "KERN_CRIT");
printk(KERN_ERR     "KERN_ERR");
printk(KERN_WARNING "KERN_WARNING");
printk(KERN_NOTICE  "KERN_NOTICE");
printk(KERN_INFO    "KERN_INFO");
printk(KERN_DEBUG   "KERN_DEBUG");

[sri@localhost scull]$ sudo dmesg | grep KERN
[ 3072.247079] KERN_EMERG
[ 3072.247084] KERN_ALERT
[ 3072.247087] KERN_CRIT
[ 3072.247089] KERN_ERR
[ 3072.247092] KERN_WARNING
[ 3072.247093] KERN_NOTICE
[ 3072.247096] KERN_INFO
[ 3072.247097] KERN_DEBUG

[sri@localhost scull]$ uname -a
Linux localhost.localdomain 3.16.6-203.fc20.x86_64 #1 SMP Sat Oct 25 12:44:32 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux