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Properties of console loglevel, and how to use it.

• include/
  • linux/
    • printk.h
• lib/
  • Kconfig.debug
• init/
  • main.c
• kernel/
  • sysctl.c
  • printk/
    • printk.c
• Documentation/
  • admin-guide/
    • parameters.txt

• /etc/sysctl.conf
• /sys/module/printk/parameters
• /proc/sys/kernel/printk/*

loglevel=       All Kernel Messages with a loglevel smaller than the
                console loglevel will be printed to the console. It can
                also be changed with klogd or other programs. The
                loglevels are defined as follows:

                0 (KERN_EMERG)          system is unusable
                1 (KERN_ALERT)          action must be taken immediately
                2 (KERN_CRIT)           critical conditions
                3 (KERN_ERR)            error conditions
                4 (KERN_WARNING)        warning conditions
                5 (KERN_NOTICE)         normal but significant condition
                6 (KERN_INFO)           informational
                7 (KERN_DEBUG)          debug-level messages

ignore_loglevel [KNL]
                Ignore loglevel setting - this will print /all/
                kernel messages to the console. Useful for debugging.
                We also add it as printk module parameter, so users
                could change it dynamically, usually by
                /sys/module/printk/parameters/ignore_loglevel.

int console_printk[4] = {
	CONSOLE_LOGLEVEL_DEFAULT,	/* console_loglevel */
	MESSAGE_LOGLEVEL_DEFAULT,	/* default_message_loglevel */
	CONSOLE_LOGLEVEL_MIN,		/* minimum_console_loglevel */
	CONSOLE_LOGLEVEL_DEFAULT,	/* default_console_loglevel */
};

/* printk's without a loglevel use this.. */
#define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT

/* We show everything that is MORE important than this.. */
#define CONSOLE_LOGLEVEL_SILENT  0 /* Mum's the word */
#define CONSOLE_LOGLEVEL_MIN	 1 /* Minimum loglevel we let people use */
#define CONSOLE_LOGLEVEL_DEBUG	10 /* issue debug messages */
#define CONSOLE_LOGLEVEL_MOTORMOUTH 15	/* You can't shut this one up */

/*
 * Default used to be hard-coded at 7, quiet used to be hardcoded at 4,
 * we're now allowing both to be set from kernel config.
 */
#define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT
#define CONSOLE_LOGLEVEL_QUIET	 CONFIG_CONSOLE_LOGLEVEL_QUIET

extern int console_printk[];

#define console_loglevel (console_printk[0])
#define default_message_loglevel (console_printk[1])
#define minimum_console_loglevel (console_printk[2])
#define default_console_loglevel (console_printk[3])

static inline void console_silent(void)
{
	console_loglevel = CONSOLE_LOGLEVEL_SILENT;
}

static inline void console_verbose(void)
{
	if (console_loglevel)
		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
}

config CONSOLE_LOGLEVEL_DEFAULT
	int "Default console loglevel (1-15)"
	range 1 15
	default "7"
	help
	  Default loglevel to determine what will be printed on the console.

	  Setting a default here is equivalent to passing in loglevel=<x> in
	  the kernel bootargs. loglevel=<x> continues to override whatever
	  value is specified here as well.

	  Note: This does not affect the log level of un-prefixed printk()
	  usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT
	  option.

config CONSOLE_LOGLEVEL_QUIET
	int "quiet console loglevel (1-15)"
	range 1 15
	default "4"
	help
	  loglevel to use when "quiet" is passed on the kernel commandline.

	  When "quiet" is passed on the kernel commandline this loglevel
	  will be used as the loglevel. IOW passing "quiet" will be the
	  equivalent of passing "loglevel=<CONSOLE_LOGLEVEL_QUIET>"

config MESSAGE_LOGLEVEL_DEFAULT
	int "Default message log level (1-7)"
	range 1 7
	default "4"
	help
	  Default log level for printk statements with no specified priority.

	  This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
	  that are auditing their logs closely may want to set it to a lower
	  priority.

	  Note: This does not affect what message level gets printed on the console
	  by default. To change that, use loglevel=<x> in the kernel bootargs,
or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value.

static int __init debug_kernel(char *str)
{
        console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
        return 0;
}

static int __init quiet_kernel(char *str)
{
        console_loglevel = CONSOLE_LOGLEVEL_QUIET;
        return 0;
}

early_param("debug", debug_kernel);
early_param("quiet", quiet_kernel);

static int __init loglevel(char *str)
{
        int newlevel;

        /*
         * Only update loglevel value when a correct setting was passed,
         * to prevent blind crashes (when loglevel being set to 0) that
         * are quite hard to debug
         */
        if (get_option(&str, &newlevel)) {
                console_loglevel = newlevel;
                return 0;
        }

        return -EINVAL;
}

early_param("loglevel", loglevel);