Install from existing Linux

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Warning: This page is being worked on at the moment and should be stabilized by Oct. 18 2013 at 6pm EST

This document describes the bootstrapping process required to install Arch Linux from a running Linux host system. After bootstrapping, the installation proceeds as described in the Installation Guide.

Installing Arch Linux from a running Linux is useful for:

The goal of the bootstrapping procedure is to setup an environment from which arch-install-scripts (such as pacstrap and arch-root) run. This goal is achieved by installing arch-install-scripts natively on the host system, or setting up an Arch Linux-based chroot.

If the host system runs Arch Linux, installing arch-install-scripts is straightforward.

On other distributions, the process is more complicated (described in #Alternative: Install arch-install-scripts natively on non Arch distro). For these distributions, it is recommended to set up a chroot instead.

Note: This guide requires that the existing host system be able to execute the new target Arch Linux architecture programs. In the case of an x86_64 host, it is possible to use i686-pacman to build a 32-bit chroot environment. See Arch64 Install bundled 32bit system. However it is not so easy to build a 64-bit environment when the host only supports running 32-bit programs.

Arch Linux-based chroot

The Arch Linux chroot environment will be used to run pacstrap. pacstrap will initiate the actual Arch Linux installation. There are three methods to setup the chroot explained below.

Method 1: Using the Bootstrap Image

  • Extract this tarball. If you have enough memory, you can extract it into a tmpfs file system.
 In the example below, we'll assume that it will be extracted to /tmp/root.x86_64/.
  • Create your partitions and mount them under /tmp/root.x86_64/mnt/.
  • If you have bash 4 or later installed, run
  # /tmp/root.x86_64/bin/arch-chroot /tmp/root.x86_64/
 If you don't have bash 4, run the following commands:
  # cp /etc/resolv.conf /tmp/root.x86_64/etc
  # mount --rbind /proc /tmp/root.x86_64/proc
  # mount --rbind /sys /tmp/root.x86_64/sys
  # mount --rbind /dev /tmp/root.x86_64/dev
  # mount --rbind /run /tmp/root.x86_64/run
    (assuming /run exists on your system)
  # chroot /tmp/root.x86_64/
  • In the chroot, run
  # Create your partitions and mount them under /tmp/root.x86_64/mnt/.
  # pacman-key --init
  # pacman-key --populate archlinux
  • Follow the Arch Linux installation guide
  https://wiki.archlinux.org/index.php/Installation_Guide#Install_the_base_system
 starting at the "Install the base system" step.

Download the bootstrap image which is a tarball containing the arch-install-scripts. It is a smaller image. Just expand the tarball into the directory of your choice (if sufficient RAM is available, to a directory in /tmp) Use the included arch-chroot to chroot into your install "system".

  • The root image can be found on one of the mirrors under either arch/x86_64/ or arch/i686/ depending on the desired architecture

Method 2: Using the LiveCD Image

It is possible to mount the root image of the latest Arch Linux installation media and then chroot into it. This method has the advantage of providing you with a working Arch Linux installation right within your host system without the need to prepare it by installing specific packages.

Note: Before proceeding, make sure the latest version of squashfs is installed on the host system. Otherwise you will get errors like: FATAL ERROR aborting: uncompress_inode_table: failed to read block.
  • The root image can be found on one of the mirrors under either arch/x86_64/ or arch/i686/ depending on the desired architecture. The squashfs format is not editable so we unsquash the root image and then mount it.
  • To unsquash the root image, run
# unsquashfs -d /squashfs-root root-image.fs.sfs
  • Now you can loop mount the root image
# mkdir /arch
# mount -o loop /squashfs-root/root-image.fs /arch
  • Before chrooting to it, we need to set up some mount points and copy the resolv.conf for networking.
# mount -t proc none /arch/proc
# mount -t sysfs none /arch/sys
# mount -o bind /dev /arch/dev
# mount -o bind /dev/pts /arch/dev/pts # important for pacman (for signature check)
# cp -L /etc/resolv.conf /arch/etc #this is needed to use networking within the chroot
  • Now everything is prepared to chroot into your newly installed Arch environment
# chroot /arch bash

Method 3: Assembling the chroot Manually (with a script)

The script creates a directory called archinstall-pkg and downloads the required packages in it. It then extracts them in the archinstall-chroot directory. Finally, it prepares mount points, configures pacman and enters a chroot.

CHROOT_DIR=archinstall-chroot Must Change First, or you might ruin your /etc/

archinstall-bootstrap.sh
#!/bin/bash
# This script is inspired on the archbootstrap script.

PACKAGES=(acl attr bzip2 curl expat glibc gpgme gnupg libarchive libassuan libgcrypt libgpg-error libssh2 lzo2 openssl pacman xz zlib pacman-mirrorlist coreutils bash grep gawk file filesystem tar ncurses readline libcap util-linux pcre arch-install-scripts)
# Change the mirror as necessary
MIRROR='http://mirrors.kernel.org/archlinux' 
# You can set the ARCH variable to i686 or x86_64
ARCH=`uname -m`
LIST=`mktemp`
CHROOT_DIR=archinstall-chroot
DIR=archinstall-pkg
mkdir -p "$DIR"
mkdir -p "$CHROOT_DIR"
# Create a list with urls for the arch packages
for REPO in core community extra; do  
        wget -q -O- "$MIRROR/$REPO/os/$ARCH/" |sed  -n "s|.*href=\"\\([^\"]*\\).*|$MIRROR\\/$REPO\\/os\\/$ARCH\\/\\1|p"|grep -v 'sig$'|uniq >> $LIST  
done
# Download and extract each package.
for PACKAGE in ${PACKAGES[*]}; do
        URL=`grep "$PACKAGE-[0-9]" $LIST|head -n1`
        FILE=`echo $URL|sed 's/.*\/\([^\/][^\/]*\)$/\1/'`
        wget "$URL" -c -O "$DIR/$FILE" 
        xz -dc "$DIR/$FILE" | tar x -k -C "$CHROOT_DIR"
done
# Create mount points
mkdir -p "$CHROOT_DIR/dev" "$CHROOT_DIR/proc" "$CHROOT_DIR/sys" "$CHROOT_DIR/mnt"
mount -t proc proc "$CHROOT_DIR/proc/"
mount -t sysfs sys "$CHROOT_DIR/sys/"
mount -o bind /dev "$CHROOT_DIR/dev/"
mkdir -p "$CHROOT_DIR/dev/pts"
mount -t devpts pts "$CHROOT_DIR/dev/pts/"

# Hash for empty password  Created by doing: openssl passwd -1 -salt ihlrowCo and entering an empty password (just press enter)
echo 'root:$1$ihlrowCo$sF0HjA9E8up9DYs258uDQ0:10063:0:99999:7:::' > "$CHROOT_DIR/etc/shadow"
echo "root:x:0:0:root:/root:/bin/bash" > "$CHROOT_DIR/etc/passwd" 
touch "$CHROOT_DIR/etc/group"
echo "myhost" > "$CHROOT_DIR/etc/hostname"
test -e "$CHROOT_DIR/etc/mtab" || echo "rootfs / rootfs rw 0 0" > "$CHROOT_DIR/etc/mtab"
[ -f "/etc/resolv.conf" ] && cp "/etc/resolv.conf" "$CHROOT_DIR/etc/"
sed -ni '/^[ \t]*CheckSpace/ !p' "$CHROOT_DIR/etc/pacman.conf"
sed -i "s/^[ \t]*SigLevel[ \t].*/SigLevel = Never/" "$CHROOT_DIR/etc/pacman.conf"
echo "Server = $MIRROR/\$repo/os/$ARCH" >> "$CHROOT_DIR/etc/pacman.d/mirrorlist"

chroot $CHROOT_DIR /usr/bin/pacman -Sy 
chroot $CHROOT_DIR /bin/bash


Using the Bootstrapped Environment

Once you are inside the chroot environment This chroot is able to execute the arch install scripts. The destination partitions should be mounted under the /mnt directory from this chroot

Initializing pacman keyring

To continue, pacman keys need to be setup according to pacman-key#Initializing the keyring. In particular some entropy need to be collected. The following two commands must be run.

# pacman-key --init
# pacman-key --populate archlinux

Mount

Remember to mount the destination partition under the /mnt of the chroot.

pacstrap

# pacstrap /mnt base

On Debian based host systems this script produces the following error:

# pacstrap /mnt base
# ==> Creating install root at /mnt
# mount: mount point /mnt/dev/shm is a symbolic link to nowhere
# ==> ERROR: failed to setup API filesystems in new root

On the host system, /dev/shm points to /run/shm. However, in the Arch-based chroot, /run/shm does not exist and the link is broken. To correct this error, create a directory /run/shm inside the chroot environment.

Edit the fstab file

Probably the genfstab script won't work. In that case, you'll need to edit the /mnt/etc/fstab file by hand. You can use the content of /etc/mtab as reference.

Replacing an Existing System Taking the Whole Partition

If you manage to get ~500MB of free space somewhere on the disk (e.g. by partitioning a swap partition) you can install the new Arch Linux system there, reboot into the newly created system and rsync the entire system to the primary partition. Fix the bootloader configuration before rebooting.

Alternative: Install arch-install-scripts natively on non Arch distro

Warning: This method is potentially difficult, your mileage may vary from distro to distro.

Download pacman source code and pacman packages

Visit the pacman homepage: https://www.archlinux.org/pacman/#_releases and download the latest release.

Now, download the following packages:

Install dependencies

Using your distribution mechanisms, install the required packages for pacman and the arch install scripts. libcurl, libarchive, fakeroot, xz, asciidoc, wget, and sed are among them. Of course, gcc, make and maybe some other "devel" packages are necessary too.

Compile pacman

  • Decompress the pacman source code and cd inside.
  • Execute configure, adapting the paths as necessary:
     ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var --enable-doc

If you get errors here, chances are you are missing dependencies, or your current libcurl, libarchive or others, are too old. Install the dependencies missing using your distro options, or if they are too old, compile them from source.

  • Compile
    make
  • If there were no errors, install the files
    make install
  • You may need to manually call ldconfig to make your distro detect libalpm.

Prepare configuration files

Now is time to extract the configuration files. Change the x86_64 as necessary.

  • Extract the pacman.conf and makepkg.conf files from the pacman package, and disable signature checking:
    tar xJvf pacman-*-x86_64.pkg.tar.xz etc -C / ; sed -i 's/SigLevel.*/SigLevel = Never/g' /etc/pacman.conf
  • Extract the mirror list:
    tar xJvf pacman-mirrorlist-*-any.pkg.tar.xz -C /
  • Enable some mirrors on /etc/pacman.d/mirrorlist
  • Extract the arch-install-scripts
    tar xJvf arch-install-scripts-*-any.pkg.tar.xz -C /

Another option is using the alien tool to convert the pacman-mirrorlist and arch-install-scripts (but no pacman) to native packages of your distro.

Replacing the Existing System without a LiveCD

If you manage to get ~500MB of free space somewhere on the disk (e.g. by partitioning a swap partition) you can install the new Arch Linux system there, reboot into the newly created system and rsync the entire system to the primary partition. Fix the bootloader configuration before rebooting.