Install from existing Linux - ArchWiki

# Install from existing Linux

Related articles

- Install from SSH

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:

- remotely installing Arch Linux, e.g. a (virtual) root server
- replacing an existing Linux without a LiveCD (see #Replacing the Existing System without a LiveCD)
- creating a new Linux distribution or LiveCD based on Arch Linux
- creating an Arch Linux chroot environment, e.g. for a Docker base container
- rootfs-over-NFS for diskless machines

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.

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 idea is to run an Arch system inside the host system. The actual installation is then executed from this Arch system. This nested system is contained inside a chroot. Two methods to setup and enter this chroot are presented below, from the easiest to the most complicated.

Note: The host system must run Linux 2.6.32 or later.
Note: Select only one of the following two methods and then read the rest of the article to complete the install.

### Creating the chroot

#### Method 1: Using the Bootstrap Image (recommended)

Download the bootstrap image from a mirror:

     $ curl -O https://mirrors.kernel.org/archlinux/iso/2015.02.01/archlinux-bootstrap-2015.02.01-x86_64.tar.gz

Extract the tarball:

     # cd /tmp
     # tar xzf <path-to-bootstrap-image>/archlinux-bootstrap-2015.02.01-x86_64.tar.gz

Select a repository server:

     # nano /tmp/root.x86_64/etc/pacman.d/mirrorlist

Note: If bootstrapping an i686 image from an x86_64 host system, also edit `/tmp/root.i686/etc/pacman.conf` and explicitly define `Architecture = i686` in order for pacman to pull the proper i686 packages.

Enter the chroot

- If bash 4 or later is installed:

      # /tmp/root.x86_64/bin/arch-chroot /tmp/root.x86_64/

- Else run the following commands:

      # cd /tmp/root.x86_64
      # cp /etc/resolv.conf etc
      # mount --rbind /proc proc
      # mount --rbind /sys sys
      # mount --rbind /dev dev
      # mount --rbind /run run
        (assuming /run exists on the system)
      # chroot /tmp/root.x86_64 /bin/bash

#### 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 a working Arch Linux installation right within the 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 errors like the following are to be expected: `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 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 the newly installed Arch environment

    # chroot /arch bash

### Using the chroot Environment

#### Initializing pacman keyring

Before starting the installation, pacman keys need to be setup. Before running the following two commands read pacman-key#Initializing the keyring to understand the entropy requirements:

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

#### Installation

Follow Installation guide#Mount the partitions and Installation guide#Install the base packages.

##### Debian-based host

On Debian-based host systems, `pacstrap` 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

In Debian, /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:

    # mkdir /run/shm

##### Fedora-based host

On Fedora based hosts and live USBs you may encounter problems when using `genfstab` to generate your fstab. Remove duplicate entries and the "seclabel" option where it appears, as this is Fedora-specific and will keep your system from booting normally.

#### Configure the system

From that point, simply follow the Mount the partitions section of the Installation guide and following sections.

## Replacing the Existing System without a LiveCD

Find ~650MB of free space somewhere on the disk, e.g. by partitioning a swap partition. If less than 600mb are available, examine the packages in the group base, and select only those required to get a system with internet connection up and running in the temporary partition. This will mean explicitly specifying individual packages to pacstrap, as well as passing it the -c option, to get packages downloaded to the host system to avoid filling up valuable space.

Once the new Arch Linux system is installed, reboot into the newly created system, and rsync the entire system to the primary partition. Fix the bootloader configuration before rebooting.

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- Getting and installing Arch