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NOTE: CentOS Enterprise Linux 5 is built from the Red Hat Enterprise Linux source code. Other than logo and name changes CentOS Enterprise Linux 5 is compatible with the equivalent Red Hat version. This document applies equally to both Red Hat and CentOS Enterprise Linux 5.

22.7. Kernel-Related Information

includes a modification to the way the Linux kernel timer interrupt is handled. Normally, a hardware timer is set to generate periodic interrupts at a fixed rate (100 times a second for most architectures). These periodic timer interrupts are used by the kernel to schedule various internal housekeeping tasks, such as process scheduling, accounting, and maintaining system uptime.

While a timer-based approach works well for a system environment where only one copy of the kernel is running, it can cause additional overhead when many copies of the kernel are running on a single system (for example, as z/VM(R) guests). In these cases, having thousands of copies of the kernel each generating interrupts many times a second can result in excessive system overhead.

Therefore, now includes the ability to turn off periodic timer interrupts. This is done through the /proc/ file system. To disable periodic timer interrupts, issue the following command:

 echo 0 > /proc/sys/kernel/hz_timer

To enable periodic timer interrupts, issue the following command:

 echo 1 > /proc/sys/kernel/hz_timer

By default, periodic timer interrupts are disabled.

Periodic timer interrupt states can also be set at boot-time; to do so, add the following line to /etc/sysctl.conf to disable periodic timer interrupts:

 kernel.hz_timer = 0


Disabling periodic timer interrupts can violate basic assumptions in system accounting tools. If you notice a malfunction related to system accounting, verify that the malfunction disappears if periodic timer interrupts are enabled, then submit a bug at (for malfunctioning bundled tools), or inform the tool vendor (for malfunctioning third-party tools).

  Published under the terms of the GNU General Public License Design by Interspire