Red Hat Enterprise Linux 5 Administration Unleashed

432CHAPTER 21Monitoring and Tuning the KernelLISTING 21.4NUMA Statisticsnode3 node2 node1 node0numa_hit 2246949 2628316 2088387 2741816numa_miss 0 0 0 0numa_foreign 0 0 0 0interleave_hit 38494 39397 39650 39722local_node 2217592 2597994 2056904 2713781other_node 29357 30322 31483 28035Using AltSysRq to Execute System RequestsWhen your system seems unresponsive or is unresponsive to other monitoring tools,using system requests can be useful to diagnose the problem. System requests are activatedby special key combinations. When activated, anyone at the console can executethese system requests without being logged into the system and without entering additionalauthentication information. Thus, it should only be enabled to diagnose problemswith the system and when the physical system is in a secure location or being monitoredby an administrator.To enable, execute the following command:echo 1 > /proc/sys/kernel/sysrqAs previously discussed, modifying the value of a /proc virtual file with the echocommand takes effect immediately but does not save the change after the system isrebooted. To make the change persist after a reboot, add the following line to/etc/sysctl.conf:kernel.sysrq=1If this file is modified, either execute the sysctl -p command to enable immediately oruse the echo command to modify the value of the virtual file.To execute these system requests on an x86 or x86_64 system, use the key combinationAlt-SysRq-. Most modern keyboards have the SysRq key labeled. If yoursdoes not, it is the same as the PrintScreen key. Key combinations for other architecturesvary. However, on any architecture, you can always use the echo command to change thevalue of /proc/sysrq-trigger to the “command key” part of the key combination. Forexample, to execute the Alt-SysRq-m system request, use the following command:echo m > /proc/sysrq-triggerTable 21.2 lists the available command keys for executing system requests.