Displaying debug level printk messages in systemd

[greg@kroah.com (Greg KH)]

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.