CODEWITHSUNDEEP
linuxlinux-kerneldevice-driverkernel-modulekernel
Vikrant
Vikrant

Reputation: 43

About to print KERNEL messages on terminal

According to manual page it told that if priority of message's log level is higher than default set log level then it will be printed on terminal. But when I had used sentence like

printk(KERN_ALERT " MESSAGE ")

I am facing problem to print message on terminal. Because the default priority is set to 4 and KERN_ALERT has priority 1, which is higher.

So, how can I print message on terminal?

Upvotes: 3

Views: 8873

Answers (3)

Dinesh M. Bhoyar
Dinesh M. Bhoyar

Reputation: 1

I faced same problem initially developing skeleton drivers on host system. every time I had to check with "dmesg" command.

I have to edit /proc/sys/kernel/printk .

For getting message on Terminal with window manager such ad KED and Gnome run "tail -f /var/log/kern.log &" to get messages on terminal.

It helped me in Ubuntu system. Hope it will help :)

Upvotes: 0

Shahbaz
Shahbaz

Reputation: 47583

I know that this doesn't exactly answer your question, but like I said in the comments, making printk log to the console is generally not a good idea. This is an alternative I suggest that should well enough serve your purpose.

Since you want to use it for debug purposes, you could simply open a new terminal and execute the following command:

tail -f /var/log/messages

or 

tail -f /var/log/dmesg

or the like. tail -f would print the last messages in the file, but would keep waiting for updates. As soon as there are more lines written in the file, tail -f would write them to console for you.

Regardless of whether you use this method or directly print to console, you may also be interested in defining a macro that calls printk and in debug mode would also put a small msleep after to make sure the log makes it to the screen, in case of crashes. This is done like this:

set_current_state(TASK_INTERRUPTIBLE);
msleep(/* amount in milliseconds */);

Upvotes: 2

Federico
Federico

Reputation: 3892

It should print messages to the console, not to the terminal. Sometimes the console and the terminal seems the same, but it is not. Edit /proc/sys/kernel/printk to set up the lowest priority to print in console

Upvotes: 3

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