printk(9) Kernel Functions printk(9)NAMEprintk - 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 ALSOregister_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.
Linux DDI $Date:$ printk(9)
