Handbook:X86/Blocks/Booting

Booting the installation media

Once the installation media is ready, it is time to boot it. Insert the media in the system, reboot, and enter the motherboard's firmware user interface. This is usually performed by pressing a keyboard key such as DEL, F1, F10, or ESC during the Power-On Self-Test (POST) process. The 'trigger' key varies depending on the system and motherboard. If it is not obvious use an internet search engine and do some research using the motherboard's model name as the search keyword. Results should be easy to determine. Once inside the motherboard's firmware menu, change the boot order so that the external bootable media (CD/DVD disks or USB drives) are tried before the internal disk devices. Without this change, the system will most likely reboot to the internal disk device, ignoring the newly attached bootable media.

Important
When installing Gentoo on a system with an UEFI firmware interface, ensure the live image has been booted in UEFI mode. In the accidental event that DOS/legacy BIOS boot was initiated, then it will be necessary to reboot in UEFI mode before finalizing the Gentoo Linux installation.

Ensure that the installation media is inserted or plugged into the system, and reboot. A GRUB boot prompt should be shown with various boot entries. At this screen, Enter will begin the boot process with the default boot options. To boot the installation media with customized boot options, such as passing additional kernel parameters or the following hardware options, highlight a boot entry, then press the e key to edit the boot entry. Make the necessary modification(s), then press ctrl+x or F10 to boot the modified entry.

Note
In all likelihood, the default gentoo kernel, as mentioned above, without specifying any of the optional parameters will work just fine. For boot troubleshooting and expert options, continue on with this section. Otherwise, just press Enter and skip ahead to Extra hardware configuration.

At the boot prompt, users get the option of displaying the available kernels (F1) and boot options (F2). If no choice is made within 15 seconds (either displaying information or using a kernel) then the installation media will fall back to booting from disk. This allows installations to reboot and try out their installed environment without the need to remove the CD from the tray (something well appreciated for remote installations).

Specifying a kernel was mentioned. On the Minimal installation media, only two predefined kernel boot entries are provided. The default option is called gentoo. The other being the -nofb variant; this disables kernel framebuffer support.

The next section displays a short overview of the available kernels and their descriptions:

Kernel choices

gentoo: Default kernel with support for K8 CPUs (including NUMA support) and EM64T CPUs.
gentoo-nofb: Same as gentoo but without framebuffer support.
memtest86: Test the system RAM for errors.

Alongside the kernel, boot options help in tuning the boot process further.

Hardware options

acpi=on: This loads support for ACPI and also causes the acpid daemon to be started by the CD on boot. This is only needed if the system requires ACPI to function properly. This is not required for Hyperthreading support.
acpi=off: Completely disables ACPI. This is useful on some older systems and is also a requirement for using APM. This will disable any Hyperthreading support of your processor.
console=X: This sets up serial console access for the CD. The first option is the device, usually ttyS0, followed by any connection options, which are comma separated. The default options are 9600,8,n,1.
dmraid=X: This allows for passing options to the device-mapper RAID subsystem. Options should be encapsulated in quotes.
doapm: This loads APM driver support. This also requires that acpi=off.
dopcmcia: This loads support for PCMCIA and Cardbus hardware and also causes the pcmcia cardmgr to be started by the CD on boot. This is only required when booting from PCMCIA/Cardbus devices.
doscsi: This loads support for most SCSI controllers. This is also a requirement for booting most USB devices, as they use the SCSI subsystem of the kernel.
sda=stroke: This allows the user to partition the whole hard disk even when the BIOS is unable to handle large disks. This option is only used on machines with an older BIOS. Replace sda with the device that requires this option.
ide=nodma: This forces the disabling of DMA in the kernel and is required by some IDE chipsets and also by some CDROM drives. If the system is having trouble reading from the IDE CDROM, try this option. This also disables the default hdparm settings from being executed.
noapic: This disables the Advanced Programmable Interrupt Controller that is present on newer motherboards. It has been known to cause some problems on older hardware.
nodetect: This disables all of the autodetection done by the CD, including device autodetection and DHCP probing. This is useful for debugging a failing CD or driver.
nodhcp: This disables DHCP probing on detected network cards. This is useful on networks with only static addresses.
nodmraid: Disables support for device-mapper RAID, such as that used for on-board IDE/SATA RAID controllers.
nofirewire: This disables the loading of Firewire modules. This should only be necessary if your Firewire hardware is causing a problem with booting the CD.
nogpm: This disables gpm console mouse support.
nohotplug: This disables the loading of the hotplug and coldplug init scripts at boot. This is useful for debugging a failing CD or driver.
nokeymap: This disables the keymap selection used to select non-US keyboard layouts.
nolapic: This disables the local APIC on Uniprocessor kernels.
nosata: This disables the loading of Serial ATA modules. This is used if the system is having problems with the SATA subsystem.
nosmp: This disables SMP, or Symmetric Multiprocessing, on SMP-enabled kernels. This is useful for debugging SMP-related issues with certain drivers and motherboards.
nosound: This disables sound support and volume setting. This is useful for systems where sound support causes problems.
nousb: This disables the autoloading of USB modules. This is useful for debugging USB issues.
slowusb: This adds some extra pauses into the boot process for slow USB CDROMs, like in the IBM BladeCenter.

Logical volume/device management

dolvm: This enables support for Linux's Logical Volume Management.

Other options

debug: Enables debugging code. This might get messy, as it displays a lot of data to the screen.
docache: This caches the entire runtime portion of the CD into RAM, which allows the user to umount /mnt/cdrom and mount another CDROM. This option requires that there is at least twice as much available RAM as the size of the CD.
doload=X: This causes the initial ramdisk to load any module listed, as well as dependencies. Replace X with the module name. Multiple modules can be specified by a comma-separated list.
dosshd: Starts sshd on boot, which is useful for unattended installs.
passwd=foo: Sets whatever follows the equals as the root password, which is required for dosshd since the root password is by default scrambled.
noload=X: This causes the initial ramdisk to skip the loading of a specific module that may be causing a problem. Syntax matches that of doload.
nonfs: Disables the starting of portmap/nfsmount on boot.
nox: This causes an X-enabled LiveCD to not automatically start X, but rather, to drop to the command line instead.
scandelay: This causes the CD to pause for 10 seconds during certain portions the boot process to allow for devices that are slow to initialize to be ready for use.
scandelay=X: This allows the user to specify a given delay, in seconds, to be added to certain portions of the boot process to allow for devices that are slow to initialize to be ready for use. Replace X with the number of seconds to pause.

Note
The bootable media will check for no* options before do* options, so that options can be overridden in the exact order specified.

Now boot the media, select a kernel (if the default gentoo kernel does not suffice) and boot options. As an example, we boot the gentoo kernel, with dopcmcia as a kernel parameter:

boot:gentoo dopcmcia

Next the user will be greeted with a boot screen and progress bar. If the installation is done on a system with a non-US keyboard, make sure to immediately press Alt+F1 to switch to verbose mode and follow the prompt. If no selection is made in 10 seconds the default (US keyboard) will be accepted and the boot process will continue. Once the boot process completes, the user is automatically logged in to the "Live" Gentoo Linux environment as the root user, the super user. A root prompt is displayed on the current console, and one can switch to other consoles by pressing Alt+F2, Alt+F3 and Alt+F4. Get back to the one started on by pressing Alt+F1.