Displaying debug level printk messages in systemd

[listmail368@gmail.com (Orion Agali)]

On 07/12/2015 12:36 AM, Greg KH wrote:
> On Sat, Jul 11, 2015 at 11:06:30PM +1000, Orion Agali wrote:
>> I'm using Arch and I cannot figure out how to get printk debug messages to
>> display in journalctl.
>>
>> I tried the following:
>>   * Set LogLevel=debug in /etc/systemd/systemd.conf
>>   * Add kernel parameter 'debug' on boot
>>   * Setting loglevel=8 in /proc/sys/kernel/printk
>>   * dmsg -n 8
>>
>> Consider the following module:
>>
>> ----------
>> #include <linux/module.h>
>> #include <linux/kernel.h>
>> #include <linux/init.h>
>> static int __init task1_init(void)
>> {
>>     pr_notice("I am at level notice");
>>     pr_debug("I am at level debug.");
>>     return 0;
>> }
>> static void __exit task1_exit(void){}
>> module_init(task1_init);
>> module_exit(task1_exit);
>> ------------
>>
>> The notice level is printed but the debug level is not.
>> The debug message is not in dmesg or /dev/kmsg either
>>
>> The answer is probably straight forward, but I've hit a wall so I'm hoping
>> somebody here will be able to point me in the right direction
> Take a look at Documentation/dynamic-debug-howto.txt for how to get
> pr_debug() working properly for your module.
>
Great reference!

After reading and testing I realize I can
  * activate at compile time using -DDEBUG
  * use dyndbg in the module paramaters
  * add queries to <debugfs>/dynamic_debug/control
  * use dyndbg in the boot string

Thank you.