some questions about log level

hi all: my questions are below: 1. Can I temporarily let kernel message show in stdout? I google some key word as "console_loglevel" and I found following methods: a. echo 8 > /proc/sys/kernel/printk b. write a simple program which calling "klogctl(8, NULL, level)" Then I purposely connect/disconnect USB, but my console keep quiet. But dmesg shows connect/disconnect messages. 2. what is differences between above a and b methods? Are they not to used to change console_loglevel? 3. is it possible the max level of "console_loglevel" doesn't mean it will show on stdout? -- Thanks for your help