| D.4. Installing Ubuntu from a Unix/Linux System | ||
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Appendix D. Random Bits | 
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| D.4. Installing Ubuntu from a Unix/Linux System | ||
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Appendix D. Random Bits |
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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.
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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. |
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
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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
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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. |
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[22]. 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
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
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.
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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.
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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.
Now it's required to install some additionally required packages, like makedev (needed for the next section):
apt install makedev
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.
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
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
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.
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.
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.)
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.
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
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
Use the adduser command to create a new user account:
# adduser myusername
You will be prompted for a full name and a password.
The normal Ubuntu configuration is to allow this new user to administer the
system using sudo. To set this up, first create an
admin group and add your new user to it:
# addgroup --system admin # adduser myusername admin
You can now use the visudo command to add these lines to
the end of /etc/sudoers, so that any user in the
admin group can administer the system:
# Members of the admin group may gain root privileges %admin ALL=(ALL) ALL
If you don't want to follow this configuration, then remember to set a root password:
# passwd root
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| D.3. Disk Space Needed |  |
D.5. Installing Ubuntu using PPP over Ethernet (PPPoE) |