Red Hat Enterprise Linux 5 Administration Unleashed

Enabling NMI Watchdog for Locked Systems 445For the last two commands, instead of using the bitmask, the -c option can beused to specify the processors, where is a comma-separated list of processornumbers. The numbering starts at 0. So, 0 represents the first processor, 1 represents thesecond processor, and so on. A hyphen can be used to list sequential processor numberssuch as 2-4.21Enabling NMI Watchdog for Locked SystemsIf you are experiencing hard system locks where the computer, even the keyboard, stopsresponding, it can be quite frustrating and difficult to diagnose. However, if you have anx86 and x86_64 system with APIC (Advanced Programmable Interrupt Controller), youmost likely have a system capable of producing NMI (Non Maskable Interrupts) even ifthe system seems locked and unresponsive. The kernel can execute these interrupts andgenerate debugging information about the locked system.NOTENMI watchdog and OProfile (discussed in Chapter 22, “Monitoring and TuningApplications”) cannot be run simultaneously. OProfile will automatically disable NMIwatchdog if it is enabled when the OProfile daemon is started.NMI watchdog has two modes:. Local APIC: capable of generating inter-processor interrupts and external processorinterrupts. I/O APIC: capable of producing interrupts from I/O buses and redirecting them tothe local APICTo enable profiling and NMI watchdog, add the profile=2 and watchdog=1 boot optionsto the kernel line of the /etc/grub.conf boot loader configuration file for the defaultboot stanza being used as shown in Listing 21.7. The kernel line has been divided intotwo lines with a backward slash (\) for printing purposes. The content should be all onone line in your configuration file.LISTING 21.7Enabling Profiling and NMI Watchdogdefault=0timeout=5splashimage=(hd0,0)/grub/splash.xpm.gzhiddenmenutitle Red Hat Enterprise Linux (2.6.17-1.2174smp)root (hd0,0)kernel /vmlinuz-2.6.17-1.2174smp ro root=/dev/sda1 rhgb \quiet profile=2 nmi_watchdog=1initrd /initrd-2.6.17-1.2174smp.img