What are the "acpi" and "noapic" kernel boot options?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 4

Issue

  • What are the acpi and noapic kernel boot options?

Resolution

ACPI

ACPI stands for Advanced Configuration and Power Interface. It is the system that controls hardware actions such as the dynamic speed fans, the power button behavior, system sleep states, and helps to identify some system capabilities.

ACPI power-saving features are hierarchical, meaning that any device running "behind" another will be dependent on the power state of the parent device. For example, a device cannot be running in full-power "behind" a device that is sleeping or in stand-by mode.

However, many hardware platforms ship with buggy or out-of-specification ACPI firmware which can cause any number of unspecified problems. If the machine is randomly powering off or failing to boot, disabling ACPI may help.

The consequences are that when ACPI is off, the server will be unable to turn itself off, as the soft shutdown cannot work after executing poweroff or shutdown -h now. It will be necessary to press/hold the shutdown/reboot button of that server, or power off via Out-of-Band management.

APIC

APIC stands for Advanced Programmable Interrupt Controller.

APIC is the replacement for the old PIC chip that, in the past, was embedded on motherboards and allowed the configuration of interrupts for peripherals like soundcards, IDE controllers, sharing/redirecting of interrupts. Disabling APIC removes the ability to make use of IRQ sharing or device IRQ remapping.

Applying boot options

By default, both features are enabled in the kernel, and can be disabled with the respective boot options acpi=off and noapic as shown below.

  • Edit /boot/grub/grub.conf

  • Edit the kernel line and add the desired option. The following example disables both ACPI and APIC:

    kernel /vmlinuz-2.6.18-194.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet noapic acpi=off
    
  • Restart your system.

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.

6 Comments

I have a question regarding this statement:

"However, many hardware platforms ship with buggy or out-of-specification ACPI firmware which can cause any number of unspecified problems. If the machine is randomly powering off or failing to boot, disabling APIC may help."

did you mean:

"However, many hardware platforms ship with buggy or out-of-specification ACPI firmware which can cause any number of unspecified problems. If the machine is randomly powering off or failing to boot, disabling ACPI may help."

thanks,

Hi Enrique,

Ah yes, it was a typo. I've corrected the article. Thank you very much for pointing it out!

I have a question regarding this statement: What version of acpi specification does RHEL6&7 follow? And which RHEL version does ACPI 6.1 start to be supported?

Off the top of my head I am not sure. Recommend opening a support case to ask this question.

I noticed that this hinders Intel's HyperThreading feature. By using acpi=off and enabling HT, we don't get to see all the cores. By removing it from grub, we can see in /proc/cpu all the "additional" cores. Is that expected?

That seems odd to me. You might want to open a support case to investigate.