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Install Ubuntu alongside Windows option appears only when unallocated space has been shrunk from C drive of Windows.

Why does it have to be only 4 drives including unallocated to dual boot?

Zanna
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Ritesh Suvarna
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    See My laptop already has 4 primary partitions: how can I install Ubuntu? http://askubuntu.com/questions/149821/my-laptop-already-has-4-primary-partitions-how-can-i-install-ubuntu But if you have Windows in BIOS boot mode, drive has to be MBR(msdos) with the 4 primary partition limit.windows only boots from newer computers using UEFI from a gpt partitioned drive. – oldfred Jun 13 '17 at 14:28

2 Answers2

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why does it have to be only 4 drives

I think you meant "partitions". And the answer is because the MBR style partition table has a maximum number of 4 partitions. Do note that you can get around this by using logical partitions.

However, GUID partition tables remove this restriction.

Now as for:

why do I have to shrink the C drive partition of windows to install Ubuntu in dual boot?

Because Ubuntu (or any Linux distro for that matter) cannot be installed onto an NTFS partition. (Well, okay technically there's WUBI but you really don't want to use that)

Zanna
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You'reAGitForNotUsingGit
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Partitioning a disk is a big part of installing a dual boot Linux.

I have a couple of dual boot systems that I setup. One has Ubuntu & W10, and uses 3 partitions for windows (system, C: and recovery) like this (from lsblk):

/dev/sda1 - System /dev/sda2 - /mnt/C or C: /dev/sda3 - /home/[user name]/Shared /dev/sda4 - Extended /dev/sda5 - [Swap] /dev/sda6 - / /dev/sda7 - /home

and the other has Debian Linux & W10 with these 10 partitions:

/dev/sda1 - System /dev/sda2 - /mnt/C or C: /dev/sda3 - /home/[user name]/Shared /dev/sda4 - Extended /dev/sda5 - [Swap] /dev/sda6 - / /dev/sda7 - /tmp /dev/sda8 - /var /dev/sda9 - /home/[user name]/Media /dev/sda10 - /home

You'll also want to be using blkid to help you setup fstab. And I start with fdisk to do the basic partitioning, but then use gparted to do the formatting and labeling which is so important to get right. I've tried all of the various partitioning tools, and these two seem to get the job done the best.

The reason for so many partitions came down to two things.

1) I wanted to be able to easily transition from W10 and needed a shared partition that both OS's could access for both reading and writing. Actually on this I have two shared partitions: Shared and Media. I found that my Media (pictures, video & audio) didn't change as much and was large and so to speed the backups and because I didn't need to backup Media as often I made it a separate partition. While you can read W10 from Linux, you don't want to write to it. This is because of the way W10 handles file permissions. /tmp and /var also have less backup needs so I split them off. Note that Shared and Media are NTFS formatted, while Swap is just swap, and /, /home/, /var, and /tmp are Linux formatted. In my case I chose btrfs for / and /home (because I wanted to do hot backups someday), and ext3 for /tmp and /var (because they need to be smaller and faster).

2) You'll need to figure out how to backup your system, which is not so easy. I backup my W10 w/ Acronis, and have a custom mybackup.sh which uses rsync to backup the Linux partitions. Without a good backup/restore option a little fire can burn down your house, and so this is a big priority to get working early on. ... and to do a full test of! One suggestion I have is to keep a 2nd identical main drive, and clone it from your working drive. It will allow you to recover until you have a better backup/recovery in place.

Important: You will want to figure out how to tell W10 to behave itself and not do a fast boot which is required for dual boot to work. Go to control panel (not the settings gear) and find Advanced power options, then disable Allow Hybrid Sleep.

Once you have your dual boot installed:

I tried for awhile having Firefox, Chrome, Thunderbird, and MariaDB all be able to share the same files in booth different OS's. If the version you use on both sides is the same they will work, but I found that keeping the version the same in both places just became too much of a pain, so now only have MariaDB sharing the same databases, and even that is a pain because any change on it in Linux requires that I reset permission when back in Windows to get the MySQL service to be able to run. I ended up using a bind mount to fool MariaDB into using a shared NTFs partition for data because after much trial and error it was the only way I could get it to work.

Now I've probably given you too much info, but I thought it might be helpful to see what someone else has done.

Elliptical view
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