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printk

NAME

printk - print messages to console log

SYNOPSIS

#include <linux/kernel.h>

int printk(const char*fmt, ...)

DESCRIPTION

Print a formatted message to the kernel console, much like the printf function of the stdio library. Normally, the message is written to the physical console device of the computer, although this behavior can be changed with the register_console function. Messages are also stored in a message log book.

The generated string may also start with a message priority code, which sets the priority of the message. The priority code strings are of the form <n> where n is a number from 0 - 7. The following macros are defined in the <linux/kernel.h> header file:

KERN_EMERG

System is unuseable

KERN_ALERT

Action must be taken immediately

KERN_CRIT

Critical conditions

KERN_ERR

Error conditions

KERN_WARNING

Warning conditions

KERN_NOTICE

Normal but significant condition

KERN_INFO

Informational

KERN_DEBUG

Debug-level messages

For example

 
         printk(KERN_NOTICE "Hello, world.\n");
 
 

does the expected thing.

RETURN VALUE

Returns the number of characters written to the log.

AVAILABILITY

Linux 1.0+

SEE ALSO

register_console(9), syslog(2)

kernel/printk.c

AUTHOR

Stephen Williams (steve@icarus.com)

BUGS

float and double formats are not supported. Floats and doubles do not belong inside the kernel anyhow.

The printk implementation protects itself from interruption, so in principle it can be used in interrupts handlers and critical sections. However, there are no guarantees about the console function that is registered.