How to Dual boot with Ubuntu? on existing Windows installation.

Get Ubuntu running alongside your existing Windows installation.

Most users who want to try Ubuntu already have desktop PCs or laptops with the Windows OS. Ubuntu can be installed alongside Windows, and both systems will coexist just fine, without interfering with each other. Ubuntu’s installation wizard has an advanced disk partition stage, where you can either trust the installer to automatically shrink the Windows partition and let Ubuntu use the freed space, or do it manually. Shrinking NTFS partitions from Linux is considered stable enough, and if you didn’t have any problems with your C drive in Windows (such as severe fragmentation), Ubuntu would resize it correctly. The installer will create the mandatory root partition (/) in the free disk area and sometimes also create separate partitions for user data (/home) and swap space. After the installer copies Ubuntu files to the root partition, it’ll perform post-installation arrangements and install the GRUB2 boot loader into the master boot record (MBR) of the hard drive on older systems, or GRUB2-EFI into the dedicated FAT32 partition on modern systems with Windows 8 or 10 and a GPT-formatted drive. The Ubuntu installer supports the Secure Boot feature of many modern Windows PCs and installs the GRUB2-EFI bootloader correctly. After rebooting, you’ll see the GRUB2/GRUB2-EFI interface, where you can choose Ubuntu or Windows. You can access Windows files from Ubuntu, but not vice versa.

Ubuntu running Windows installation

Dare to go for manual setup Ubuntu’s installation program has been polished in recent years and now looks very smooth. Soon after completing basic steps (like language selection), a user faces the first real obstacle during the ‘Installation type’ step. You can see that Ubuntu has automatically detected our Windows 7 copy and offered the simple solution that does not require any extra user input. If so, you let the installer automatically guess what OS you already have and how to keep it intact. It’s safe, and you’ll be able to define how much space you want to allocate for Ubuntu in the next step. Note the second option with the red Warning label – we are going to install Ubuntu and keep Windows working, so do not choose this. The last option is a path to a more expert-like drive allocation program. Dual-booting in UEFI mode introduces more routines for the Ubuntu installer. If you’re unsure what to choose, go with Auto mode. If your system uses a BIOS interface, you can repartition your drive manually.

Define the space for Ubuntu

Make sure you give it enough disk space.

The automatic partitioning option in the Ubuntu installer is more comfortable for non-tech savvy users, but it does have certain limitations, such as the inability to add an extra Home partition or define the swap space manually. Let’s use the fully fledged partitioning method by choosing the ‘Something else’ option in the previous step, or by clicking the ‘Advanced partitioning tool’ link in the ‘simple’ mode. First, you’ll need to resize the NTFS volume and make it smaller by some number of gigabytes. Make sure that you don’t have excessive hard disk fragmentation in Windows. Otherwise you may turn your NTFS volume in Ubuntu installer unusable. Try to guess how much space you’ll need in the unallocated area after shrinking. For instance, 10GB looks like the bare minimum – go with at least twice as much as that for the Ubuntu root partition. Think ahead to cover aspects like swapping and a separate partition for /home.

Create Ubuntu partitions

Options for partitioning your hard drive

Many older articles concerning the installation of Linux strongly advise users to create a swap partition with a size twice that of the RAM volume (for instance, 2GB if you have 1GB of RAM). However, modern computers have larger amounts of RAM, and therefore, this rule is not that important anymore. That being said, you could go without the swap partition altogether unless you feel that you need it. The separate partition for your home folder in Ubuntu is another aspect to consider. If you go with a single root partition, that means all your personal files and settings will be kept together with the rest of the system on a single partition (/), just like if you only had the C: drive in Windows for storing everything. Sometimes it is more sensible to create another partition and mount it as /home – this means that your files and settings will not get lost, even if you decide to reinstall or remove Ubuntu in the future.

Select target drive for the bootloader.

This option only requires your attention if it’s the case that you have more than one hard drive inside or attached to your computer. Otherwise, if you had previously installed custom operating systems onto your Windows desktop PC or laptop, you might find it useful to get to grips with this option as well. First of all, to boot correctly, Ubuntu needs a properly installed GRUB bootloader.

You can install it on a hard drive (e.g., /dev/sda) or on a drive partition (eg /dev/sda3). If you have a relatively modern UEFI/Secure Boot setup, then Ubuntu will act differently: it will install GRUB2-EFI on /dev/sda1, which is a FAT32 partition, and mount it as /boot/efi. Furthermore, a special loader entry in your computer’s UEFI internals will be made by the means of the ‘efibbotmgr’ utility. Don’t worry, though; Ubuntu does all of this automatically.

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