Do I have to make a partition before installing dual-boot Ubuntu?

Question

I am trying to dual boot Ubuntu and Windows 10. On the guides I have seen online, people generally make a disk partition prior to installation. Then on the installation screen when they are asked whether to install alongside Windows, erase Windows, or "something else" they click the last option and select their pre-made partition. Why not just select the first option and let Ubuntu handle the partitioning? If I have to make the partition myself and select the correct partition myself, I feel that only increases the potential for making mistakes which could lose data as I am not particularly good with computers.

Answer 1

There is no need to pre-partition the disk before installing Ubuntu.

Ubuntu's installer has a step which lets you partition/organize/format your disk. All it needs is to have unallocated space on the disk, meaning space that is not part of any existing partition.

However, with automatic installation your options of choosing partition sized are very limited, which is why many people choose to do manual partitioning of the disk.

This requires more knowledge about Ubuntu and its use of partitions, so it's much simpler to just let it use the entire space automatically, especially when creating a virtual machine.

Answer 2

TL;DR

• Always have backups of everything you can't afford to loose.
• Unallocated space is NOT a partition.

Whenever installing an additional OS it is and always has been strongly recommended to have backups. Even seasoned users make mistakes sometimes and there's always an inherent risk of data loss when managing partitions.

When dual-booting with Windows prior to Windows 8 it was considered generally safe to use the automatic "install alongside" option whenever Windows was working properly and there were no logical errors or excessive fragmentation in the Windows system partition ("C:").

However, since the advent of Windows 8 and its infamous Fast Startup feature - in essence, hibernation - additional precautions are now recommended. Namely, disabling the aforementioned feature is a must before proceeding to the Linux distro installation. This allows correct detection of drives, partitions and OS.

Furthermore, the sentence people generally make a disk partition prior to installation is an equivocation. Do not confuse unallocated space with a partition. It's generally recommended, now more then ever, to use Windows tools to shrink one or more Windows partitions, typically "C:" (system partition) and/or some data partition (letters may vary but typically "D:") to make room for Ubuntu. This results in unallocated space, not a new partition. You can't create suitable partitions for a Linux installation anyway.

Having now unallocated space you can either choose "something else" for manual partitioning - safe as long as you DON'T delete any partition - to create all the required partitions (currently only a new root and selecting the preexisting ESP) or the desired partitions for advanced users that have a reason for doing it. For most users the automatic partitioning is indeed recommended and that can be done with the "install alongside" option but, again, provided that there's unallocated space, not just Windows partitions. Letting the installer shrink Windows partitions is no longer recommended even with Fast Startup disabled, always do it previously, from Windows, using the Windows native tools.

Summary:

• Always have proper backups;
• Shrink one or more Windows partitions with Windows tools, from Windows, before starting the installer. Recovery and/or diagnostic tools partitions should be left untouched.
• Either select the "install alongside" option for automatic partitioning upon detection of the presence of unallocated space, or select "something else" for manual partitioning. In this case, for any modern uEFI based machine don't forget to select (don't format!) the ESP - EFI System Partition - as well.