How to create a separate /boot partition after installation when dual booting?

Question

I dual boot Arch Linux and Ubuntu. I have the following partition setup:

Here sda1 is where Ubuntu is installed, Arch on sda2. New Partition #2 is the proposed /boot. sda4 is a common home for both the OS.

The grub was installed by Arch. I would like to create a separate /boot partition for encrypting the root filesystems of both the OSes.

I am following this guide on Community Wiki, and have a few questions.

The guide is written for 10.04 and does not mention anything about dual booting. Will it still work? I already have 500 MB of unallocated free space which I can use for /boot. Then why should I use the live disk? Can't I do everything from my current Ubtunu installation?

This is what I understand. /boot partition can't be shared between operating systems. Since I require /boot for my Arch, I should copy the contents of /boot from Arch to the newly created /boot from Ubuntu. Now I can reboot to Arch. Then I should change the fstab of arch to mount the new /boot. Then I install GRUB on the /boot partition from Arch. Should I make any changes to Ubuntu's fstab? Will this break Ubuntu?

If what intend to do is wrong, how do I do this?

Solution

You can not create more that 4 primary partitions in MBR.

I suggest temporarily removing /sda3 swap partition.

1. Move left side of /sda4 right.

2. Remove /sda3.

3. Create an extended partition in unallocated space.

4. Create two partitions inside the extended.

5. Format one as swap, the other as ext2 for /boot.

6. Update /etc/fstab with new UUIDs and mount points for swap and /boot.

You will have to update /etc/fstab in both Arch and Ubuntu to mount the new partition as /boot and also copy there contents of both boot directories.

You will also need to re-install grub after that.

These operations can be done while booted from Ubuntu LiveUSB.

But it will be much easier to have two separate /boot partitions for each OS.

And also ext3 is not a good choice for /boot. I would recommend ext2.

ext3 is similar to ext4 but obsolete. ext2 does not have journal, it works faster. Journal is not that important for /boot.

So there is not reason to use ext3. You can choose between default ext4 or ext2.

Comments

[daltonfury42]

@Pilot6 Done! xx

[Pilot6]

Is it an MBR partition table or GPT?

[Pilot6]

And where is 500 MB unallocated?

[daltonfury42]

@Pilot6, You caught my lie. I will resize swap to get the 500 mb. I will change the question. It's MBR.

[Ron]

Boot partition can be shared between distros, but managing it is painful!

[daltonfury42]

I did a repartitioning before seeing your answer. I've updated the question. Thanks for the answer, but it does not answer my question.

[Pilot6]

@daltonfury42 Got you. I will try to give some guide.

[daltonfury42]

Thanks, one more clarification. Why not seperate /boot for Arch with the grub and a non-seperate /boot for ubuntu? Maybe if I do it like this, I won't have to touch Ubuntu installation. The grub will detect Ubuntu and load it. Is that OK?

[Pilot6]

You can do this way too. Grub should detect all OSes.

[daltonfury42]

Wait. I am doing all this to encrypt Ubuntu. If so, the /boot of Ubuntu will be encrypted. Won't it make Ubuntu unbootable?

[Pilot6]

What is the point of encrypting /boot?

[daltonfury42]

Let us continue this discussion in chat.

[daltonfury42]

Why ext3 is not a good choice and ext2 is recommended?