Pour que la console n'affiche plus de message d'erreur à chaque fois que la souris sort de l'écran virtuel, on peut ajouter dans /etc/sysctl.conf :

kernel.printk = 4 4 1 7

et ne pas oublier d'activer par :
sysctl -p

Explication http://www.mjmwired.net/kernel/Documentation/sysctl/kernel.txt et http://lists.debian.org/debian-user/2008/02/msg00457.html:
The four values in printk denote : console_loglevel, default_message_loglevel, minimum_console_loglevel and default_console_loglevel respectively.

These values influence printk() behavior when printing or logging error messages. See 'man 2 syslog' for more info on the different loglevels.

- console_loglevel: messages with a higher priority than this will be printed to the console
- default_message_level: messages without an explicit priority will be printed with this priority
- minimum_console_loglevel: minimum (highest) value to which console_loglevel can be set
- default_console_loglevel: default value for console_loglevel

Les niveaux sont :
#define KERN_EMERG "<0>" /* system is unusable */
#define KERN_ALERT "<1>" /* action must be taken immediately */
#define KERN_CRIT "<2>" /* critical conditions */
#define KERN_ERR "<3>" /* error conditions */
#define KERN_WARNING "<4>" /* warning conditions */
#define KERN_NOTICE "<5>" /* normal but significant condition */
#define KERN_INFO "<6>" /* informational */
#define KERN_DEBUG "<7>" /* debug-level messages */