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Boot Options

When and How to Use

There are at least major two cases where one may wish to use boot options.

Case 1: When trying to install, and the install freezes.

Case 2: After a system has been installed and does not boot or the system needs adjustment.

When installing

When your installer/live CD loads you will come to this page:

Go ahead and hit the F6 key.

After you hit F6 you will see a screen that looks like this:

Simply append the options you want to the end of the line. This will mean that you get to turn off or alter the way the machine boots. Here is an example of adding an option:

For Installed Systems That Need Adjustment

This will explain how to edit the grub menu entries on the fly (not permanently).

This assumes of course that have installed grub, the default boot loader in Ubuntu. (This article does not deal with alternatives like lilo.)

As the machine starts to boot you get a Grub message, at this time press the ESC key. This drops you to a text menu. Choose the boot option you want to work with. Navigate using the the up and down arrow keys. (Cursor key.)

When you have selected the menu item press 'e'.

Then you will be presented with a "root" line on the first line. You must then move to the "kernel" line one down from there with the down arrow. then again you press 'e'.

Go to the end of the line (ctrl-E) and add the command from below.

Press the enter key when you are done with the changes, and finally press 'b' to boot.

Your machine will now hopefully boot.

Options for the boot command line.

This list is not comprehensive but it contains some of the common options. When presented with the text on the screen "boot:" then the options below can be given. They must have the kernel name before the option.

Example: Adding the vga=771 option

boot: /boot/vmlinuz-2.6.15-26-k7 root=/dev/hda1 ro quiet splash

boot: /boot/vmlinuz-2.6.15-26-k7 root=/dev/hda1 ro quiet splash vga=771

Options can be used together such as in this example:

/boot/vmlinuz-2.6.15-26-k7 root=/dev/hda1 ro quiet splash noapic nolapic

Kernel Options

These options are used by the kernel, and will apply to any system at any time.

Option: vga=xxx

Impact: Set your framebuffer resolution to VESA mode xxx. Check here for a list of possible modes.

Option: acpi=off OR noacpi

Impact: This parameter disables the whole ACPI system. This may prove very useful, for example, if your computer does not support ACPI or if you think the ACPI implementation might cause some problems (for instance random reboots or system lockups).

Option: acpi=force

Impact: Activates the ACPI system even if your computer BIOS date is older than 2000. This parameter overwrites acpi=off and can also be used with current hardware if the ACPI support is not activated despite apm=off.

Option: pci=noacpi OR acpi=noirq

Impact: These parameters disable the PCI IRQ routing

Option: pci=acpi

Impact: This parameter activates the PCI IRQ routing

Option: acpi_irq_balance

Impact: ACPI is allowed to use PIC interrupts to minimize the common use of IRQs.

Option: acpi_irq_nobalance

Impact: ACPI is not allowed to use PIC interrupts.

Option: acpi=oldboot

Impact: Deactivates the ACPI system almost completely; only the components required for the boot process will be used.

Option: acpi=ht

Impact Deactivates the ACPI system almost completely; only the components required for hyper threading will be used.

Option: noapic

Impact: Disable the "Advanced Programmable Interrupt Controller (APIC)".

Option: nolapic

Impact: Disable the "local APIC".

Option: apm=off OR noapm

Impact: Disable the Advanced Power Management.

Option: irqpoll

Impact: Changes the way the kernel handles interrupt calls (set it to polling). Can be useful in case of hardware interrupt issues.

Installer options (user-land)

These options are usually used when installing a system, and are picked up by the installer program or start-up scripts, and not by the kernel.

Option: debian-installer/framebuffer=false

Impact: Disable framebuffer.

Option: hw-detect/start_pcmcia=false

Impact: Don't start PCMCIA. Personal Computer Memory Card International Association, one of the stranger names for a piece of hardware. :-) Your hardware is an association.

Option: netcfg/disable_dhcp=true

Impact: Force static network config.

Option: bootkbd=uk

Impact: Set keyboard map. Use a two letter ISO country code to get the right letters on the right keys. This option can help with password problems.

(This list is far from complete, please feel free to add some options.)

Permanent changes

Once you know you need to boot with a special option on your installed system, you'll have to edit the file /boot/grub/menu.lst to make the boot option permanent.

To to this please do the following:

sudo nano /boot/grub/menu.lst

Add the option to the line that starts with "# kopt=". Then run

sudo update-grub

to have the menu entries updated.

NB! If you instead edit the menu entries directly, your changes will magically disappear the next time update-grub is run, for instance when system packages are updated.