noapic - what exactly does it do?

Asked by Sposh

My laptop (Lenovo 3000 V100) would occasionally freeze during boot (setting up the network). I read on some forums that this might be fixed using the noapic option in Grub. It worked like a charm, no problems so far.

However I _would_ like to know exactly what I've done. I know that APIC stands for "Advanced Programmable Interrupt Controller" (not to be confused with ACPI, which is in charge of hardware recognition & power management). So what is going on when I disable it? What is being used instead (if anything), PIC? Am I making any sacrifices? Everything seems to be in place and working - why would I ever want an Advanced PIC if the normal one seems to the the job fine?

This is not an urgent or life-or-death question - I managed to fix my problem OK - just curious... Cheers.

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Frode M. Døving (frode) said :


I think this might help you understand what it is:

- Frode

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Sposh (launchpad-net-sposh) said :

That link is pretty much what I've been reading up to now; but it doesn't really explain what I'm missing out on if I disable it (or what is being used instead, if anything, to control the interrupts).

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Mackenzie Morgan (maco.m) said :

When the battery gets really low it won't automatically suspend or hibernate. The screen won't dim when you take it off of AC power. And I'm not sure about this one, but the fan might not turn on when it gets hot.

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Sposh (launchpad-net-sposh) said :

Isn't that what would happen with turning off ACPI rather than APIC? I just tried unplugging the laptop and the screen did dim...

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Alan Pope 🍺🐧🐱 🦄 (popey) said :

Yes, Sposh, ACPI does the power management and button press detection. ACPI is completely different. I am not sure we are the best people to answer questions about how a particular technology works. You are probably best speaking to the developers, hanging out on the Linux Kernel Mailing List (LKML) or in some other way talking to some deeply technical people.

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Best Sposh (launchpad-net-sposh) said :

Doing another search I came up with MS' take on it:

"Key Benefits of the I/O APIC"

It seems to be that APIC is a Very Good Idea if you are running multiple processors. Even on single processors you may find your hardware go a bit slower. There are also vaguer mentions of "sharing interrupts is bad" and "APIC architecture is superior". Anyways, none of these matter to me too much. If noapic makes booting up smoother, so be it. Thanks to all who pitched in time to answer.

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Mackenzie Morgan (maco.m) said :

Guess my anwer was evidence that PCMCIA (people can't memorize computer industry acronyms) :p Is it really necessary to have 2 acronyms that use the same letters?

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Ordinary12 (kendallbrown) said :

I'm trying to install from the alternative Edgy Eft 6.10 cd but I keep getting hung once I see the brown wall paper. Could this be a case where I need to enter the noapic command? If so....where in the installation program shoul I enter this command?

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Sposh (launchpad-net-sposh) said :

Don't have my laptop here at the moment, so this is a post that relies on some pretty unreliable memory...

When you still see the Ubuntu logo, ie, before all the Gnome stuff starts? Yes, you can try. Edit the /boot/grub/menu.lst file (as superuser: sudo gedit /boot/grub/menu.lst) - make sure you make a backup copy first just in case. Near the end of the file are all the boot menu options, you need to edit the line beginning with "kernel" on the menu item giving you problems. As a first test you can remove the "quiet" option - and maybe "splash"? - (to see what is going on behind the pretty wallpaper) and reboot - this will give you a clue on exactly where it is hanging.

The kernel line will be something like this:

kernel /boot/vmlinuz-2.6.17-10-generic root=/dev/sda5 ro quiet

Just add noapic at the end:

kernel /boot/vmlinuz-2.6.17-10-generic root=/dev/sda5 ro quiet noapic

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jedioetzi (jedioetzi) said :

the advantages of apic are for dual core processors too?