Gentoo 1.4_rc2 in RedHat 8.0 using UML

1.Introduction

This document describes one case to install Gentoo Linux 1.4_rc2 into RedHat 8.0 using User Mode Linux.

Gentoo in RedHat? Yes, actually. If you want to try Gentoo and you have free partition in your disk, you can install Gentoo just by following the standard installation procedure (e.g. one for x86). But some of you cannot do it due to lack of free partition or disk, just because you have already assigned entire disk space to your former installation. You would have some other reason to leave the current OS. In those cases, UML (User Mode Linux) will be a choice. UML is a linux kernel runs as a non-root user process. Necessary filesystems are given as files. You can install any distribution using UML if its installer works well on UML. But it seems that always some hacks are necessary for it because an installer has to check devices automatically but UML doesn't have it.

If you are using Gentoo and want to run UML with Gentoo, see Gentoo Linux Developer's guide to system testing with User-Mode Linux . If you are using rpm-based distro and plan to run UML with rpm-based distro, UML Builder will help you a lot. But I wanted to install Gentoo but leave RedHat as I used before. I found no document targetting such specific case, so I thought it would be nice to write a document for it.

I didn't research so deeply why these steps are required. I just followed the boot sequence and added some steps required on UML. In case you find faster/simpler procedure than I wrote, please give me a feedback.

2.Goal

1. Install Gentoo 1.4_rc2 into UML on RedHat 8.0 in an x86 machine.
2. Without compiling UML kernel. Use the standard UML kernel 2.4.19-5um provided in the RPM file available from UML Project.

3.Preparation

Summary in short 

This chapter describes what to be prepared to boot up the installer in UML.

file	deescription
gentoo-basic-x86-1.4_rc2.iso	LiveCD ISO image
initrd	RAM disk image to boot at first
livecd	filesystem for installation: converted from /livecd.cloop in the ISO image filesystem
rootfs_gt1.4	root filesystem for UML you install Gentoo
swapfs	swap filesystem for UML

If you know how to prepare them, or you already made it and going through the procedure described in this page, go boot.

Extract initrd from ISO image 

% isoinfo -i /path/to/gentoo-basic-x86-1.4_rc2.iso -x '/ISOLINUX/INITRD.;1' > initrd

Kernel starts with initial ramdisk image (aka initrd). It is usually on a bootable intstall CD with a kernel and starts at the CD booting procedure. You will have to do it with the UML kernel. So you have to extract initrd in advance.

Retrieve cloop extractor and extract livecd 

livecd.cloop is another filesystem which contains the installation environment used after the first boot. It is mounted via the compressed loopback (aka cloop) filesystem in a normal installation procedure using LiveCD. But the standard UML kernel available at the UML project page cannot use cloop module in the LiveCD. So I decompressed it in my preparation stage so that I can easily mount it in a normal way. This section consists of two steps.

The first step is to make the decompress command. It is provided in a cloop package available at Knopper's website.

% wget http://www.knopper.net/download/knoppix/cloop_0.66-1.tar.gz
% tar xzf cloop_0.66-1.tar.gz
% cd cloop-0.66
% vi Makefile // Insert APPSONLY=1 at the top section
% make zcode
% make extract_compressed_fs
% cd ..

The second step is to extract livecd.cloop and decompress it.

% isoinfo -i /path/to/gentoo-basic-x86-1.4_rc2.iso -x '/LIVECD.CLOOP;1' > livecd.cloop
% cloop-0.66/extract_compressed_fs livecd.cloop > livecd

Install UML and extract modules for 2.4.19-5um 

Here you need to run UML with a pre-built UML kernel and a pre-built filesystem. It will not take time if you install UML using RPM file. After that, boot the UML kernel and log in as root. Please refer other documents for details to run a UML kernel with a pre-built non-Gentoo filesystem.

After starting you UML with non-Gentoo distro, you need to extract module files to avoid errors during UML network configuration for your Gentoo installation later. Just make a tarball of modules from UML.

// Get user_mode_linux-2.4.19.5um-0.i386.rpm and root_fs.rh-7.2-full.pristine.20020312 here.
% /bin/su // to become root
# rpm -ivh user_mode_linux-2.4.19.5um-0.i386.rpm
# ^D // to return to your shell
% linux ubd0=root_fs.rh-7.2-full.pristine.20020312
// Here, log in the UML system as root.
# mkdir /mnt/loop
# mount none /mnt/loop -t hostfs -o /path/to/gentoo-working-dir
# cd /
# tar cf /mnt/loop/modules-2.4.19-5um.tar lib/modules/2.4.19-um
// Shutdown the UML system.
# shutdown -h now

Create root and swap filesystem 

You will need root filesystem and swap filesystem as a normal file to install Gentoo Linux into. This example configures the size to 500MB for / and 200MB for swap.

% dd if=/dev/zero of=rootfs_gt1.4 seek=500 count=1 bs=1M
% mke2fs -F rootfs_gt1.4
% dd if=/dev/zero of=swapfs seek=200 count=1 bs=1M
% mkswap -f swapfs

Check your preparation 

Check if you get these files in your working directory.

gentoo-basic-x86-1.4_rc2.iso
initrd
livecd
rootfs_gt1.4
swapfs

4.Boot

Boot the installer with the UML kernel 

% linux \
	devfs=nomount \
	mem=96m \
	load_ramdisk=1 \
	prompt_ramdisk=0 \
	ramdisk_size=60000 \
	initrd=initrd \
	root=/dev/ram0 \
	ubd0=rootfs_gt1.4 \
	ubd1=swapfs \
	eth0=ethertap,tap0,,192.168.x.x \
	noscsi

In this "booting" there is an IP address specified in the kernel options. This is an address for tap0, which is a virtual device to route packets between the host and UML. It is okay to specify the same IP address which is assigned to the host's real device. The IP address for the UML virutla machine will be configured later.

Initial RC command 

Code listing 4.2

# /linuxrc

After invoking /linuxrc, you will be requested to select the keymap. Then, you will get an error that CD drive is not detected. That's okay because your UML kernel doesn't have any CD drive, though your host system should have.

Mount ISO image in your host 

Now you are running UML kernel with (virtually) no CD drive, but the CD image file is on your host's current directory. You can use it within UML by mounting the host's filesystem.

# mkdir -p /mnt/host
# mount none /mnt/host -t hostfs -o /path/to/gentoo-working-dir
# mount /mnt/host/gentoo-basic-x86-1.4_rc2.iso /newroot/mnt/cdrom -o loop
# mount -o ro,loop -t ext2 /mnt/host/livecd /newroot/mnt/cloop

Continue the boot process by hand 

# cd /newroot
# ln -s mnt/cloop/bin
# ln -s mnt/cloop/sbin
# ln -s mnt/cloop/boot
# ln -s mnt/cloop/usr
# ln -s mnt/cloop/opt
# mkdir initrd proc tmp
# chmod 1777 tmp 
# (cd /newroot/mnt/cloop; cp -a etc root home var lib /newroot)
# tar xf /mnt/host/modules-2.4.19-5um.tar
# echo "6" > /proc/sys/kernel/printk
# umount /proc
# pivot_root . initrd
# chroot .

5.After chroot

Configure UML network 

Code listing 5.1

# mount /proc # net-setup eth0

Important: You have to assign different IP from the UML tap's.

Warning: The author couldn't configure well on the host which has two network connections and host's eth0 was not connected. If you are trying that case, please check the routing command lines shown on the virtual console. The author recommends to use a host with only one network device.

Optional: Proxy configuration 

If you use a proxy to access outside, set these variables.

Code listing 5.2

# export http_proxy="proxy.of.company.com:1234" # export ftp_proxy="$http_proxy" # export RSYNC_PROXY="$http_proxy"

Mount filesystems for installation 

# swapon /dev/ubd/1
# mkdir /mnt/gentoo
# mount /dev/ubd/0 /mnt/gentoo
# mkdir /mnt/gentoo/proc
# mkdir /mnt/gentoo/dev
# umount /proc
# cd /mnt/gentoo
# tar xjpf /mnt/cdrom/gentoo/stage1-x86-1.4_rc2.tbz2
# mount -o bind /proc /mnt/gentoo/proc
# mount -o bind /dev /mnt/gentoo/dev
# nano -w /etc/resolv.conf
# cp /etc/resolv.conf /mnt/gentoo/etc
# chroot /mnt/gentoo /bin/bash

6.After chroot again

Try to emerge! 

# env-update // You will get an error that /etc/make.profile not found.  Just ignore it.
# source /etc/profile
# emerge sync
// Again just for sure
# env-update 
# source /etc/profile
# emerge sync // This won't take long this time.

7.Installation continues...

Here you reached just at the start line of the the normal installation from stage1 tarball.

Starting Stage1 

# cd /usr/portage
# scripts/bootstrap

Stage2 and more 

You will need to go on to the next stage. Just follow the instruction shown in Gentoo Linux 1.4_rc2 Installation Instructions.

8.Starting your UML with Gentoo 1.4_rc2

Once you install Gentoo 1.4_rc2, you can start it simply with no network configuration:

% linux ubd0=root_gt1.4 ubd1=swapfs

or with some more arguments:

% linux umid=Gentoo1.4_rc2 ubd0=root_gt1.4 ubd1=swapfs mem=128m eth0=ethertap,tap0,,192.168.x.x