Gentoo installation tips and tricks

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The Gentoo installation allows for very flexible approaches to the various installation methods. As it is almost impossible to insert every single tip or trick in the installation instructions this document tries to deal with all submitted tips and tricks for reference purposes.

This document contains various tips and tricks for the Gentoo/x86 installation. Most of them are discussed in a dense way - they are meant as an addendum to the installation instructions and not as a replacement.

Advanced Installations

Software RAID

If not familiar with software RAID, please read the Software RAID HOWTO.

Once booted from the Installation CD, load the appropriate RAID modules. For instance, if planning on using RAID-1:

root #modprobe raid1

When partitioning disks, make sure that the partitions use fd (Linux RAID autodetect) as Partition Type instead of 83 (Linux native). The partition type can be altered using the t command in fdisk.

Before creating the RAID arrays, the metadevice nodes must be created:

root #mknod /dev/md1 b 9 1
root #mknod /dev/md2 b 9 2
root #mknod /dev/md3 b 9 3

After partitioning, create the /etc/mdadm.conf file (yes, indeed, on the Installation CD environment) using mdadm, an advanced tool for RAID management. For instance, to have the boot, swap and root partition mirrored (RAID-1) covering /dev/sda and /dev/sdb, it is possible to use:

root #mdadm --create --verbose /dev/md1 --level=1 --raid-devices=2 --metadata=0.90 /dev/sda1 /dev/sdb1
root #mdadm --create --verbose /dev/md2 --level=1 --raid-devices=2 --metadata=0.90 /dev/sda2 /dev/sdb2
root #mdadm --create --verbose /dev/md3 --level=1 --raid-devices=2 --metadata=0.90 /dev/sda3 /dev/sdb3
Do not use any form of striping such as RAID-0 or RAID-5 on the boot partition. Also, the --metadata=0.90 is only necessary for these critical file systems. Other filesystems can use more recent metadata formats.

The Linux Software RAID driver will start creating the metadevices. See its progress in /proc/mdstat. Wait until the metadevices are completely finished before proceeding.

root #mdadm --detail --scan > /etc/mdadm.conf

From now onwards, use /dev/md1 for the boot partition, /dev/md2 for the swap partition and /dev/md3 for the root partition.

Right before chrooting, don't forget to copy over /etc/mdadm.conf to /mnt/gentoo/etc.

When configuring the kernel, make sure to have the appropriate RAID support in the kernel and not as module.

When installing extra tools, emerge sys-fs/mdadm as well. Note that this isn't available on all Installation CDs so it might not be possible to install Gentoo on a Software RAID when using a networkless installation!

When configuring the bootloader, make sure it gets installed in the MBR of both disks if using mirroring.

ATA RAID using 2.4 kernels

Make sure to boot the Installation CD using the doataraid option. Once booted, check the contents of /dev/ataraid. It should contain various disc* directories for each hard disk available in the ATA RAID. An entire disk is displayed as disc while partitions are part*.

Write down the various /dev/ataraid/disc*/* device files that used to install Gentoo on. Substitute the /dev/sda examples in the installation with this path.

Before chrooting, bind-mount the /dev structure in the new environment:

root #mount --rbind /dev /mnt/gentoo/dev

When configuring the kernel, make sure to enable support for the ATA RAID chipset and options. For instance, a popular ATA RAID system is a Promise FastTrack built-in RAID in which case Promise FastTrack Options will definately need to be built in into the kernel.

When configuring GRUB, first create a GRUB bootdisk. This is not particularly hard. First install GRUB as normal, but when coming to the part where GRUB is getting installed in the MBR, follow the following instructions:

root #cd /boot/grub
root #dd if=stage1 of=/dev/fd0 bs=512 count=1
root #dd if=stage2 of=/dev/fd0 bs=512 seek=1

Write the grub.conf file. This is no different from the installation instructions, just make sure that root= points to the ATA RAID device.

After finishing the installation, boot with the GRUB bootdisk. A GRUB prompt should appear. Now configure GRUB to boot from the ATA RAID device:

grub>root (hd0,x)
grub>setup (hd0)

Now reboot (with the GRUB bootfloppy removed).

LILO users can safely use the instructions mentioned in the installation instructions.

Using the Installation CD kernel

If not wanting to compile a kernel, it is possible to use the kernel from the Installation CD and copy it to the system. When coming to the point where asked to compile a kernel, go to another terminal (press Alt + F2) and log in with the root password supplied at the beginning of the installation.

Copy over the kernel and modules to the Gentoo system:

${KN} is the kernel name, usually something like 'gentoo' or 'smp'.
root #cp /mnt/cdrom/isolinux/${KN} /mnt/cdrom/isolinux/${KN}.igz /mnt/gentoo/boot
root #mkdir -p /mnt/gentoo/lib/modules
root #cp -Rp /lib/modules/`uname -r` /mnt/gentoo/lib/modules

To have all modules that are currently running (from the Installation CD) loaded during bootup of the Gentoo system, run the following command from within the chrooted environment:

root #mkdir -p /etc/modules-load.d
root #cut -d ' ' -f 1 /proc/modules >> /etc/modules-load.d/local.conf

Verify the /etc/modules-load.d/local.conf content and update appropriately.

Simplifying the installation

Leaving the terminal

Many people want to leave their system when it's compiling. In certain cases this is rather difficult as the installation is done in a public environment. If this is the case, it would be preferable perform the compilation in the background and log out from all terminals.

There are several possible solutions for this. The first one is to use screen. After booting the Installation CD, set the root password and start a screen session:

Not all Installation CDs provide screen. If this is the case, use one of the other methods described in this section.
root #screen -S gentoo

Once inside the screen session the entire installation may be performed. When leaving a terminal, press Ctrl + a, d (that is, Ctrl and a at the same time, then followed by a d) to detach the screen session. It is now safe log out of the system (without losing work).

To regain access to the terminal, log in as root again and attach to the running screen session:

root #screen -x gentoo

If screen is not an option, there is still a way to leave the terminal. Follow the installation instructions, but when a long-term compilation begins (for instance the ./scripts/ step), use nohup which allows for a process to continue even when the session closed with a log out. Don't forget the trailing "&", otherwise the process will not be placed in the background! Remember the current directory (the pwd command will show that) as this will be needed later on.

root #pwd
root #nohup ./scripts/ &

Now exit the chrooted environment (exit) and the Installation CD session. The compilation will continue in the background.

To check the compilation, log in as root (on the Installation CD) and chroot back into the environment, then go to the directory where the session was left off:

root #chroot /mnt/gentoo /bin/bash
root #env-update && source /etc/profile
root #cd /var/db/repos/gentoo

Now use the less command on the nohup.out file that is situated inside that directory. The compilation will append its output to that file, so if it is desired to follow the compilation progress, run less nohup.out and press F to follow the changes. When the compilation is finished, continue with the next step of the installation instructions.

When finished following the changes, press Ctrl + c followed by a q. This won't stop the compilation process, only the less process.

Fixing errors and issues

Extensive testing of the disks

If a disk needs to be thoroughly checked for consistency (bad sectors and such), can use the -c (that's lowercase c) option while placing the ext2/ext3/ext4 filesystem on it (using mke2fs). This will format, perform a read-test and mark all bad blocks as such. If really paranoid, use -c -c to format the disk and perform an extensive read/write test.

root #mke2fs -j -c /dev/sda3

Recovering from a malfunctioning installation

If for some reason Gentoo installation fails, it is not required to redo the installation all over again. Instead, it is possible to safely "go" to the point where an issue occurred (or where it might be suspected the instructions are flawed) and try a different approach.

First of all chroot back into the Gentoo Linux environment. Follow the instructions again, but ignore the partitioning steps as the partitions are already created and even populated. It is possible to immediately mount those partitions at /mnt/gentoo. Ignore the steps about stage extraction and modifying make.conf - so as to not overwrite files.

Once chrooted inside the Gentoo Linux environment, immediately go to the step where it is thought a different approach should be tried. Don't redo all the steps like bootstrapping and such unless that is the place where things might have gone wrong.

For instance, if suspecting a wrongly configured grub.conf, fire up an editor to update /boot/grub/grub.conf.

Once a different approach has been tried, consider how much of the subsequent steps need to be performed again. If the subsequent steps are depending on this latest change, they will need to be redone.

For instance:

  • if a variable inside make.conf has been changed, all subsequent compiling since those depend on the settings inside make.conf will need to be redone
  • if /boot/grub/grub.conf has been altered, it is possible to immediately exit the chrooted environment and reboot as no subsequent steps are depending on grub.conf
  • if the kernel has been recompiled, just make sure that the bootloader configuration points to the correct kernel image (double-check that /boot is mounted!), then exit the chrooted environment and reboot
  • if /etc/fstab changed, exit the chrooted environment and reboot

For most recovery operations, a reboot may be done immediately. Only in certain cases will the subsequent installation steps need to be redone.

This page is based on a document formerly found on our main website
The following people contributed to the original document: Xavier Neys, nightmorph
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.