Install Gentoo on a bootable USB stick (2024)

Booting Gentoo from a USB stick is really quite simple. The main challenge is to setup an initial ramdisk and to include the drivers for all the machines it is going to boot. This article describes how to install Gentoo onto a USB stick that can be booted on any computer. This installation will be just like a regular desktop installation and changes will be persistent.

Note
This article covers installation of a complete, functional, Gentoo system onto a USB drive. See the LiveUSB article for instructions on creating a simple bootable drive, that can for example be used for Gentoo installation.

Preparation

Note
The guide assumes that the current platform is a Gentoo Linux one. The majority of steps however can be performed from any distribution, just translate the Gentoo-specific way of doing things (such as installing software) to the other distribution's practices.

Start by installing a couple of necessary packages. Most importantly these are a kernel and the sys-kernel/genkernel package:

Compiling the kernel

Make the required changes to the kernel and compile it. Please see Configuring the Linux kernel and the kernel configuration guide for more detail on this step. Importantly remember that a general kernel is better here because the more general it is the more machines will boot with it.

During the configuration, it is of course possible to compile modules as these will be included in the initramfs and loaded at boot.

The above command will take some time as it will build the default kernel, create a ramdisk and then copy all files into /tmp/boot.

initramfs-genkernel-x86_64-3.5.2-gentookernel-genkernel-x86_64-3.5.2-gentooSystem.map-genkernel-x86_64-3.5.2-gentoo

Preparing the USB stick

Create 2 partitions on the drive (assuming the installation will have a /boot and a / (root) partition). We assume that the USB stick is at /dev/sdb (run dmesg immediately after plugging in the USB stick to see which device is being used).

Command (m for help): dSelected partition 1 Command (m for help): nPartition type: p primary (0 primary, 0 extended, 4 free) e extendedSelect (default p): pPartition number (1-4, default 1): 1First sector (2048-4001759, default 2048): Using default value 2048Last sector, +sectors or +size{K,M,G} (2048-4001759, default 4001759): +100M Command (m for help): nPartition type: p primary (1 primary, 0 extended, 3 free) e extendedSelect (default p): pPartition number (1-4, default 2): Using default value 2First sector (206848-4001759, default 206848): Using default value 206848Last sector, +sectors or +size{K,M,G} (206848-4001759, default 4001759): Using default value 4001759 Command (m for help): aPartition number (1-4): 1 Command (m for help): p Disk /dev/sdb: 2048 MB, 2048901120 bytes255 heads, 63 sectors/track, 249 cylinders, total 4001760 sectorsUnits = sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: 0x001663df Device Boot Start End Blocks Id System/dev/sdb1 * 2048 206847 102400 83 Linux/dev/sdb2 206848 4001759 1897456 83 Linux Command (m for help): wThe partition table has been altered! Calling ioctl() to re-read partition table.Syncing disks.

Make sure that the first partition is bootable (a command toggles the boot flag).

Now format the new partitions. In the example we use the ext2 file system but another file system for the / partition can be used if it is supported in the kernel. Notice that during the formatting operation, a label is assigned to the partitions. This is important because it will be how the root file system is detected later as the USB stick can be booted on systems where the drive letter allocation is completely different.

Gentoo stage 3 installation

With the kernel, ramdisk and file systems ready, we now need the minimal installation to be performed. This includes a fresh stage3 as well as a Portage tree snapshot.

• current-stage3
• portage-latest.tar.xz

For this example stage3-amd64-20120621.tar.bz2 and portage-latest.tar.xz are used. This next bit is the same as in the handbook for installing Gentoo.

The sections below cover those aspects of a Gentoo Linux installation that are specific to installing on an USB stick. It is recommended to use the Gentoo handbook instructions while keeping an eye on this article.

Bootloader

In order to boot the new system, install a bootloader on the USB stick.

The below sections give example configurations for either using GRUB or using lilo together with syslinux.

GRUB

Warning
This method only applies to UEFI booting!

Emerge GRUB (from within the chroot):

Install GRUB to the corresponding place with your platform information. Suppose you are running a x86_64 machine with an EFI partition mounted to /boot/efi, the following command will install GRUB onto the USB stick:

Warning
Note that the --removable option is very important. It indicates that the target location is removable device. Don't forget it otherwise you may mess up your own system!

If nothing bad happens, run grub-mkconfig to generate the GRUB configuration:

Change the target directory accordingly if you use a different GRUB config directory.

lilo

Emerge lilo (from within the chroot):

Edit etc/lilo.conf so that it has the correct information in it.

Warning
These settings are very important and will be discussed line by line.

FILE /etc/lilo.confConfigure lilo.conf

boot=/dev/sdb # The location of the USB Stick (currently)lba32 # use lba32 addressing (ignore)compact # boot quickly by loading lots of blocks # remove when there are problems with bootingprompt # Prompt for user inputtimeout=20 # Time to wait before default selectiondefault="Gentoo-352" # Default selection after timeout image=/boot/vmlinuz-5.10.76-gentoo-r1-x86_64label="Gentoo-352"read-onlyroot=/dev/ram0append="root=LABEL=GENTOO_USB_ROOT scandelay=5"initrd=/boot/initramfs-5.10.76-gentoo-r1-x86_64.img

The lines after image are all easy but the append line contains some interesting options.

• root=LABEL=GENTOO_USB_ROOT will use the label of the disk instead of /dev/sdb2 which is important because these device numbers move around depending on the number of hard disks in the computer or number of USB disk drives.
• Also important for USB booting is the scandelay option, as USB devices need a little time to be detected by the kernel; that is what this option is for. When there are lots of modules booting takes a long time so it probably does not matter, but if there are only a few modules loaded then it is important, because the system could have booted before the kernel detects the USB device. Also, on newer machines with USB3 controllers it is necessary to add the xhci_hcd driver (built into the kernel or as a module).

Now install LILO (with the configuration) on the USB stick:

Warning: /dev/sdb is not on the first diskWarning: The initial RAM disk is too big to fit between the kernel and the 15M-16M memory hole. It will be loaded in the highest memory as though the configuration file specified "large-memory" and it will be assumed that the BIOS supports memory moves above 16M.Added Gentoo-352? *2 warnings were issued.

The first warning is to be expected as we are not installing the boot loader onto the hard disk in the computer. The second warning will only cause a problem on machines that are old; if it is a problem try cutting down the kernel by removing modules.

syslinux

Warning
syslinux currently only works with ext{2,3,4}, btrfs, ntfs and fat filesystems.

Put the boot sector onto the USB stick.

Now to configure the bootloader.

FILE /boot/syslinux/syslinux.cfg

PROMPT 1TIMEOUT 50DEFAULT gentoo LABEL gentoo LINUX ../vmlinuz-5.10.76-gentoo-r1-x86_64 APPEND root=LABEL=GENTOO_USB_ROOT scandelay=3 ro INITRD ../initramfs-5.10.76-gentoo-r1-x86_64.img

Note
The ro in the above APPEND line will cause the root partition to be mounted read-only (which is usually preferred on USB sticks). Replace ro with rw to allow the system to be modified from the boot onwards (instead of having the user mount the file system as read-write later).

Next install syslinux onto the USB stick. The --device /dev/sdb1 option is not absolutely necessary though.

fstab

FILE /etc/fstabConfigure the fstab file to work with labels

LABEL=GENTOO_USB_BOOT /boot ext2 noauto,noatime 1 2LABEL=GENTOO_USB_ROOT / ext2 noatime 0 1/dev/SWAP none swap sw 0 0/dev/cdrom /mnt/cdrom auto noauto,ro 0 0/dev/fd0 /mnt/floppy auto noauto 0 0

Tips and tricks

Although it is possible to use the system just made as a standard Gentoo system, it might be worthwhile to compile binary packages on a host and then installing them on the USB stick. Or if the system has enough memory just mount /var/tmp to a tmpfs, as compilation will be much quicker that way anyway!

See also

• Installation — an overview of the principles and practices of installing Gentoo on a running system.
• LiveUSB — explains how to create a Gentoo LiveUSB or, in other words, how to emulate a x86 or amd64 Gentoo LiveCD using a USB drive.