22.3. Starting and Stopping OProfile

To start monitoring the system with OProfile, execute the following command as root:

~]# opcontrol --start

Output similar to the following is displayed:

Using log file /var/lib/oprofile/oprofiled.log Daemon started. Profiler running.

The settings in /root/.oprofile/daemonrc are used.

The OProfile daemon, oprofiled, is started; it periodically writes the sample data to the /var/lib/oprofile/samples/ directory. The log file for the daemon is located at /var/lib/oprofile/oprofiled.log.

Disable the nmi_watchdog registers

On a Red Hat Enterprise Linux 6 system, the nmi_watchdog registers with the perf subsystem. Due to this, the perf subsystem grabs control of the performance counter registers at boot time, blocking OProfile from working.

To resolve this, either boot with the nmi_watchdog=0 kernel parameter set, or run the following command to disable nmi_watchdog at run time:

~]# echo 0 > /proc/sys/kernel/nmi_watchdog

To re-enable nmi_watchdog, use the following command:

~]# echo 1 > /proc/sys/kernel/nmi_watchdog

To stop the profiler, execute the following command as root:

~]# opcontrol --shutdown