If you have disk that contains Windows installed

1. Boot from Ubuntu Installation media.


2. Unmount any mounted drives if they exist.


3. Proceed to Step 4. Choose "Something else" and click Continue:

You will see partition table. It will look like this:

4. 
   

   Free some space for Ubuntu:

   
   
   
   
   
   • Select the Windows drive (not the loader!). It should be the biggest drive in the map.
   
   
   • Click Change... button. Reduce Windows' partition to 60% of it's size. Notice that you should remain some free space on it (8 – 20 GiB should be enough).
     
     
   
   
   • If you want, you can delete some partitions. This is done by clicking - button. Do not delete Windows partition!
     
   
   
   
   

   And ~40 GiB should be kept for Ubuntu. Click OK and Continue to write changes on disk.

   
   


5. Now your partition table should look like this:

6. Now, you can proceed with steps 4 – 7 of part about blank installation. Notice that swap will be placed on logical partition. This doesn't matter, in any case it will work perfect.

If you have a OEM-preinstalled copy of Windows 8 or later

Computers with OEM installs of Windows usually come with more than 1 or 2 partitions. Starting with Windows 8 the partition table should be GPT, allowing for more than 4 primary partitions.

1. Resizing the Windows partition

There are at least 2 ways doing this:

• from the live media


• in Windows

A. Resizing from Ubuntu live media

You can run GParted or use only the manual partitioning menu of the installer.

B. The safer option: Resizing from within Windows

• 
  

  Resize the Windows partition with Disk Management (run diskmgmt.msc).

  
  
  

  

  
  
  

  Select your Windows partition and choose "Shrink Volume…" from the context menu.

  
  
  

  

  
  
  

  This will usually shrink to the minimum possible, you may want to adjust the value to leave more space for Windows.

  
  
  

  

  
  


• 
  

  Optionally disable fast startup and probably disable hibernation, if it is activated and you intend to access the Windows partition with Ubuntu. Run powercfg.cpl and navigate to Power Options > System Settings through "Choose what the power button does".

  
  
  

  

  
  
  

  

  
  
  

  

  
  

2. Manually setting up the partition layout for Ubuntu

• 
  

  Attention! No, you don't want to erase the entire disk and Windows along with it. Choose the Something else option if you see this screen. (Something else may be the most difficult option to understand, but considering existing bugs you know what you will get.)

  
  
  

  

  
  
  

  

  
  


• 
  

  You will get to the manual partitioning menu, where you should at least create a root partition (/) and a swap partition.

  
  
  

  

  
  
  
  
  
  • 
    

    Option 1: add only a root partition

    
    
    

    

    
    
  
  
  • 
    

    Option 2: add a root and home partition

    
    
    

    

    
    
  
  
  
  

  …finally add the swap partition:

  
  
  

  

  
  
  

  Note that there usually is an existing EFI System Partition (short ESP, efi in the screenshot), that the installer will automatically detect and mount to install EFI loaders and programs.

  
  
  

  

  
  

Related bug reports

• GPT partition tables are not properly detected - Ubiquity suggests erasing disk

Related

• 
  My answer to SU question: Clean install Windows 8.1 or Windows 8 from OEM key (now updated with info for Windows 10)


• Adding an encrypted partition with pam_mount during login (1, 2)

If you have md RAID

I will not cover how to create mdadm arrays here. There is a lot of articles around the Internet. However, there is one major problem: Ubiquity installer doesn't account for the arrays created in the live session, so you'll probably get unbootable system after installation on such array.

1. 
   

   Create the setup like mine:

   
   
   

   $ sudo fdisk -l
   
   
   
   Disk /dev/sda: 160.0 GB, 160041885696 bytes
   
   ...
   
   
   
      Device Boot      Start         End      Blocks   Id  System
   
   /dev/sda1            2048   156299263    78148608   83  Linux
   
   /dev/sda2       156299264   311556095    77628416    7  HPFS/NTFS/exFAT
   
   /dev/sda3   *   311556096   312580095      512000   83  Linux
   
   
   
   Disk /dev/sdb: 80.0 GB, 80026361856 bytes
   
   ...
   
   
   
      Device Boot      Start         End      Blocks   Id  System
   
   /dev/sdb1            2048   156301311    78149632   83  Linux
   
   
   
   Disk /dev/md0: 160.0 GB, 160048349184 bytes
   
   ...
   
   
   
   Disk /dev/md0 doesn't contain a valid partition table
   
   

   
   
   

   As you can guess, I created /dev/md0 mdadm array from /dev/sda1 and /dev/sdb1. It's empty now. Let's install something on it.

   
   


2. 
   

   Create partitions on /dev/md0 as you like:

   
   
   

   

   
   
   

   Important: Install /boot onto one of partition outside the array because GRUB doesn't support mdadm. In my case, it's /dev/sda3. If you want more quick booting of your system, it should be placed at the beginning of the disk.

   
   



3. Install Ubuntu. Click Continue testing. Or reboot and see initramfs prompt



4. 
   

   Now, you have to chroot into installed system and install mdadm:

   
   
   

   sudo mount /dev/md0p6 /mnt
   
   sudo mount /dev/md0p5 /mnt/home
   
   sudo mount /dev/sda3 /mnt/boot
   
   for d in /dev /proc /sys /run; do sudo mount --bind $d /mnd$d; done
   
   chroot /mnt
   
   apt-get install mdadm
   
   

   
   
   

   Installing mdadm should fix booting problem.

   
   

Do any of the following help you? (sorry, I don't have enough rep to comment this).

Now suppose that we are going to install Ubuntu 11.04 and at first of the installation process we will meet Allocate drive space screen (the most important step in the installation process). In Allocate drive space screen Select Something else to partition your disk drive manually.

The Next screen shows sda1 partition for Windows Xp and free space, Now we are going to install Ubuntu 11.04 so we need to create / partition and Swap.

Create / Partition:

Select free space and press on Add button.

Ubuntu 11.04 requires about 4.4 GB, So we should type a value more than 4.4 GB. Here in my case I put 6000 MB i.e 6 GB.

From "Use as" I selected Ext4 journalling file system.

From "Mount point" I selected /.

Press Add button to create / partition.

Create Swap:

In the previous screen select free space, and press Add button.

Swap doesn't need much space. In my case I put 500 MB

From "Use as" select Swap area

No need to Mount point.

Click Ok button to create swap.

Install:

Now we have /, partition, and swap so we are ready to install.

To start installation process press Install now button.

Manual partitioning on Ubuntu installation

For installing Windows on a separate partition, this should be fairly self explanatory from the "Install Ubuntu alongside them" option, however you may come across the following bug.

Your existing partition (Windows) is on the left, Ubuntu is on the right. That's the standard order when shrinking one partition to create another for dual-booting.

Installing Ubuntu with Windows installed on a partition

Partition shows "unknown" Used in GParted

This happened to me on 17.10 because my Windows 10 Lenovo P51 used a Logical Disk Manager (LDM) Partition.

The solution was to shrink the partition from inside Windows as shown at: https://askubuntu.com/a/521195/52975

You can then install Ubuntu on the free space allocated.

Cannot shrink disk fully

Then I hit the second problem: Windows said I had 400Gb of free space in the partition, but I could only shrink 250Gb.

The solution was to go inside Windows and:

• Disable Page File (AKA Windows' swap)


• Disable System Protection

as mentioned at: https://superuser.com/questions/1017764/how-to-shrink-a-windows-10-partition/1060508#1060508

Then after the reboot, it let me shrink it all the way.