Booting, First Time and Thenceforth
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Using, Testing, and Permanence
All of the items on this page use "kernel command line items", so-called because they are items which tell the Linux kernel to change its default behavior. They are placed into the kernel command line, either manually at bootup, or via boot configuration for automatic use at each startup. It is very possible to use many them in combination, but usually just one or two are really needed to add to the default setup.
To test any of these items, just hit F1 as the system just comes up, and you will have a prompt in which to type them.
To make them permanent, you'll need to edit /boot/grub/grub.conf as superuser. In that file, you will see at least one line which starts with the word "kernel"; at the very end of every such line, you should put the kernel command line item you wish to keep using at each boot.
Video problems: vga16, nofb
The most basic one of all of these, is probably vga16. That's all, just:
vga16
It helps in a lot of situations where there is an old or very complex video hardware. There is another which also often helps:
nofb
Devices and Hangups: pci
There is a fairly large category of kernel options for PCI behavior. If a machine behaves oddly (e.g. PCI devices that are known to work in Linux don't want to work, or the system is very slow whenever a PCI card is used), you may want to experiment with these parameters:
pci=assign-busses pci=routeirq
They can be combined with:
pci=assign-busses,routeirq
Power management: acpi=off, apm=off, and another option
In the PC hardware milieu, power management is a mess. There are actually two semiindependent power management systems out there in PC hardware, APM (older) and ACPI (newer). The problem is, both sometimes exist on the same system, and often it is hard to tell which to use, if either, because often both are buggy and/or risky to use. The hardware manufacturers have put out drivers for other operating systems which simply turn off the worthless bits, but they have not been so kind to Linux. If you are having miscellaneous problems, this one is worth trying:
acpi=off
Also for some, there is this:
apm=off
And lastly, you should definitely try turning power management as entirely off as possible in your BIOS. There are lots of buggy BIOSes.
Older AMD Duron/Athlon (K7): cpu=i686
If you're using a very old version of AMD Duron or Athlon systems (prior to Athlon-XP) and your machine crashes frequently, reinstall with
cpu=i686
This makes sure SSE instructions (that may not be present on old K7 class machines) are not being used, even if support for them has been detected.
An oddball: lapic
On many machines there is a chip or chip real estate called a "local APIC". On most it is disabled, but apparently on some machines it can be helpful. To enable it, use:
lapic
In this case, though, it is also confirmed that the LAPIC is often disabled for good reason :-) So don't make this one permanent unless you're sure.
Finding More
Often, the kernel will actually tell you what to try, if you know where to listen. From a command prompt, typing the command:
dmesg
gives you all of the kernel boot messages. And some of the above were identified in this very way. For instance, on a test laptop, we saw:
PCI: If a device doesn't work, try "pci=routeirq". If it helps, post a report
and so we began booting with pci=routeirq, and lo and behold, it did good things! To see if your dmesg contains suggestions, one way is:
dmesg | grep try
