D.4. Installing Ubuntu from a Unix/Linux System

This section explains how to install Ubuntu from an existing Unix or Linux system, without using the menu-driven installer as explained in the rest of the manual. This “cross-install” HOWTO has been requested by users switching to Ubuntu from Debian, Red Hat, Mandriva, and SUSE. In this section some familiarity with entering *nix commands and navigating the file system is assumed. In this section, $ symbolizes a command to be entered in the user's current system, while # refers to a command entered in the Ubuntu chroot.

Once you've got the new Ubuntu system configured to your preference, you can migrate your existing user data (if any) to it, and keep on rolling. This is therefore a “zero downtime” Ubuntu install. It's also a clever way for dealing with hardware that otherwise doesn't play friendly with various boot or installation media.

Note As this is a mostly manual procedure, you should bear in mind that you will need to do a lot of basic configuration of the system yourself, which will also require more knowledge of Ubuntu and of Linux in general than performing a regular installation. You cannot expect this procedure to result in a system that is identical to a system from a regular installation. You should also keep in mind that this procedure only gives the basic steps to set up a system. Additional installation and/or configuration steps may be needed. In general, this method of installation is not recommended for casual or first time users.

D.4.1. Getting Started With your current *nix partitioning tools, repartition the hard drive as needed, creating at least one filesystem plus swap. You need around 506MB of space available for a console only install. Next, create file systems on the partitions. For example, to create an ext3 file system on partition /dev/sda6 (that's our example root partition): # mke2fs -j /dev/ sda6 To create an ext2 file system instead, omit -j . Initialize and activate swap (substitute the partition number for your intended Ubuntu swap partition): # mkswap /dev/ sda5 # sync # swapon /dev/ sda5 Note Instead of using a dedicated swap partition, you may omit the swap partition setup here and later just use a swap file instead. Mount one partition as /mnt/ubuntu (the installation point, to be the root ( / ) filesystem on your new system). The mount point name is strictly arbitrary, it is referenced later below. # mkdir /mnt/ubuntu # mount /dev/ sda6 /mnt/ubuntu Note If you want to have parts of the filesystem (e.g. /usr) mounted on separate partitions, you will need to create and mount these directories manually before proceding with the next stage.

D.4.2. Install debootstrap The utility used by the Ubuntu installer, and recognized as the official way to install an Ubuntu base system, is debootstrap. It uses wget and ar, but otherwise depends only on /bin/sh and basic Unix/Linux tools . Install wget and ar if they aren't already on your current system, then download and install debootstrap. If these steps are executed under Ubuntu you can simply do this by apt install debootstrap . If you have an RPM (Red Hat Package Manager) based system, you can use alien, which is available in the Debian repositories, to convert the .deb file to a useable .rpm file. Or, you can use the following procedure to install it manually. Make a work folder for extracting the .deb into: # mkdir work # cd work The debootstrap binary is located in the Ubuntu archive (be sure to select the proper file for your architecture). Download the debootstrap .deb from the pool, copy the package to the work folder, and extract the files from it. You will need to have root privileges to install the files. # ar -x debootstrap_0.X.X_all.deb # cd / # zcat /full-path-to-work/work/data.tar.gz | tar xv

D.4.3. Run debootstrap debootstrap can download the needed files directly from the archive when you run it. You can substitute any Ubuntu archive mirror for ports.ubuntu.com/ubuntu-ports in the command example below, preferably a mirror close to you network-wise. Mirrors are listed at http://wiki.ubuntu.com/Archive. If you have an Ubuntu focal CD mounted at /cdrom , you could substitute a file URL instead of the http URL: file:/cdrom/ubuntu/ Substitute one of the following for ARCH in the debootstrap command: amd64 , arm64 , armhf , i386 , powerpc , ppc64el , or s390x . # /usr/sbin/debootstrap --arch ARCH focal /mnt/ubuntu

D.4.4. Configure The Base System Now you've got a real Ubuntu system, though rather lean, on disk. chroot into it: # LANG=C.UTF-8 chroot /mnt/ubuntu /bin/bash After chrooting you may need to set the terminal definition to be compatible with the Ubuntu base system, for example: # export TERM= xterm-color Depending on the value of TERM, you may have to install the ncurses-term package to get support for it. Note If warnings occur like: bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8) The required localization files need to be generated: # sudo locale-gen en_US.UTF-8 Generating locales (this might take a while)... en_US.UTF-8... done Generation complete. D.4.4.1. Configure Apt Debootstrap will have created a very basic /etc/apt/sources.list that will allow installing additional packages. However, it is suggested that you add some additional sources, for example for source packages and security updates: deb-src http://archive.ubuntu.com/ubuntu focal main deb http://security.ubuntu.com/ubuntu focal-security main deb-src http://security.ubuntu.com/ubuntu focal-security main Make sure to run apt update after you have made changes to the sources list. D.4.4.2. Install additional packages Now it's required to install some additionally required packages, like makedev (needed for the next section): apt install makedev D.4.4.3. Create device files At this point /dev/ only contains very basic device files. For the next steps of the installation additional device files may be needed. There are different ways to go about this and which method you should use depends on the host system you are using for the installation, on whether you intend to use a modular kernel or not, and on whether you intend to use dynamic (e.g. using udev ) or static device files for the new system. A few of the available options are: create a default set of static device files using (after chrooting) # mount none /proc -t proc # cd /dev # MAKEDEV generic or depending on your specific architecture: # MAKEDEV std # cd ..

manually create only specific device files using MAKEDEV

bind mount /dev from your host system on top of /dev in the target system, like: mount --bind dev /dev Note that the postinst scripts of some packages may try to create device files, so this option should only be used with care. D.4.4.4. Mount Partitions You need to create /etc/fstab . # editor /etc/fstab Here is a sample you can modify to suit: # /etc/fstab: static file system information. # # file system mount point type options dump pass /dev/XXX / ext3 defaults 0 1 /dev/XXX /boot ext3 ro,nosuid,nodev 0 2 /dev/XXX none swap sw 0 0 proc /proc proc defaults 0 0 sys /sys sysfs defaults 0 0 /dev/fd0 /media/floppy auto noauto,rw,sync,user,exec 0 0 /dev/cdrom /media/cdrom iso9660 noauto,ro,user,exec 0 0 /dev/XXX /tmp ext3 rw,nosuid,nodev 0 2 /dev/XXX /var ext3 rw,nosuid,nodev 0 2 /dev/XXX /usr ext3 rw,nodev 0 2 /dev/XXX /home ext3 rw,nosuid,nodev 0 2 Use mount -a to mount all the file systems you have specified in your /etc/fstab , or, to mount file systems individually, use: # mount /path # e.g.: mount /usr Current Ubuntu systems have mountpoints for removable media under /media , but keep compatibility symlinks in / . Create these as as needed, for example: # cd /media # mkdir cdrom0 # ln -s cdrom0 cdrom # cd / # ln -s media/cdrom You can mount the proc and sysfs file systems multiple times and to arbitrary locations, though /proc and /sys respectively are customary. If you didn't use mount -a , be sure to mount proc and sysfs before continuing: # mount -t proc proc /proc # mount -t sysfs sysfs /sys The command ls /proc should now show a non-empty directory. Should this fail, you may be able to mount proc from outside the chroot: # mount -t proc proc /mnt/ubuntu/proc D.4.4.5. Setting Timezone Setting the third line of the file /etc/adjtime to “UTC” or “LOCAL” determines whether the system will interpret the hardware clock as being set to UTC respective local time. The following command allows you to set that. # editor /etc/adjtime Here is a sample: 0.0 0 0.0 0 UTC The following command allows you to choose your timezone. # dpkg-reconfigure tzdata D.4.4.6. Configure Networking To configure networking, edit /etc/network/interfaces , /etc/resolv.conf , /etc/hostname and /etc/hosts . # editor /etc/network/interfaces Here are some simple examples from /usr/share/doc/ifupdown/examples : ###################################################################### # /etc/network/interfaces -- configuration file for ifup(8), ifdown(8) # See the interfaces(5) manpage for information on what options are # available. ###################################################################### # We always want the loopback interface. # auto lo iface lo inet loopback # To use dhcp: # # auto eth0 # iface eth0 inet dhcp # An example static IP setup: (broadcast and gateway are optional) # # auto eth0 # iface eth0 inet static # address 192.168.0.42 # network 192.168.0.0 # netmask 255.255.255.0 # broadcast 192.168.0.255 # gateway 192.168.0.1 Enter your nameserver(s) and search directives in /etc/resolv.conf : # editor /etc/resolv.conf A simple example /etc/resolv.conf : search hqdom.local nameserver 10.1.1.36 nameserver 192.168.9.100 Enter your system's host name (2 to 63 characters): # echo UbuntuHostName > /etc/hostname And a basic /etc/hosts with IPv6 support: 127.0.0.1 localhost 127.0.1.1 UbuntuHostName # The following lines are desirable for IPv6 capable hosts ::1 ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts If you have multiple network cards, you should arrange the names of driver modules in the /etc/modules file into the desired order. Then during boot, each card will be associated with the interface name (eth0, eth1, etc.) that you expect. D.4.4.7. Configure Locales and Keyboard To configure your locale settings to use a language other than English, install the appropriate language packs and configure them. Currently the use of UTF-8 locales is recommended. # apt install language-pack-de language-pack-gnome-de To configure your keyboard (if needed): # apt install console-setup # dpkg-reconfigure keyboard-configuration Note that the keyboard cannot be set while in the chroot, but will be configured for the next reboot.

D.4.5. Install a Kernel If you intend to boot this system, you probably want a Linux kernel and a boot loader. Identify available pre-packaged kernels with: # apt-cache search linux-image Then install the kernel package of your choice using its package name. # apt install linux-image- arch-etc (You may want install linux-image-generic , too.)

D.4.6. Set up the Boot Loader To make your Ubuntu system bootable, set up your boot loader to load the installed kernel with your new root partition. Note that debootstrap does not install a boot loader, though you can use apt inside your Ubuntu chroot to do so. Note that this assumes that a /dev/sda device file has been created. There are alternative methods to install grub2, but those are outside the scope of this appendix.

D.4.7. Remote access: Installing SSH and setting up access In case you can login to the system via console, you can skip this section. If the system should be accessible via the network later on, you need to install SSH and set up access. # apt install openssh-server Root login with password is disabled by default, so setting up access can be done by setting a password and re-enable root login with password: # passwd # editor /etc/ssh/sshd_config This is the option to be enabled: PermitRootLogin yes Access can also be set up by adding an ssh key to the root account: # mkdir /root/.ssh # cat << EOF > /root/.ssh/authorized_keys ssh-rsa .... EOF Lastly, access can be set up by adding a non-root user and setting a password: # adduser joe # passwd joe

D.4.8. Finishing touches As mentioned earlier, the installed system will be very basic. If you would like to make the system a bit more mature, there is an easy method to install all packages with “standard” priority: # apt install tasksel # tasksel install standard Of course, you can also just use apt to install packages individually. After the installation there will be a lot of downloaded packages in /var/cache/apt/archives/ . You can free up some diskspace by running: # apt clean