about pr_debug

hi all: I'm confused with pr_debug. My codes is: ########################################### #include <linux/module.h> #include <linux/kernel.h> static int __init init_page_dir(void) { pr_debug("Hello world\n"); return 0; } static void __exit exit_page_dir(void) { pr_debug("\nGoodbye now...\n\n"); } MODULE_LICENSE("GPL"); module_init(init_page_dir); module_exit(exit_page_dir); ########################################### I make it, and insmod it. But the messages of "Hello world" don't show. So, My question is If i want to fix it , I should set the *DEFAULT_MESSAGE_LOGLEVEL and * *rebuild the kernel ?* My kernel version is:2.6.18 OS is: centOS Thank you.