[UPDATE 07-18-2018] It seems that some people still get the same error message after unchecking “Install the third party software” option. If that is the case for you, you can try the following:

1. Reboot your computer with Live USB and start Ubuntu (or Linux Mint) installation again

2. At the “Installation type” step, choose “Something else”

3. Delete all partitions (since you already have trouble installing Ubuntu, I don’t think you need to worry about losing data)

4. Manually create partitions. You will need at least three partitions as follows:

• Main partition for Ubuntu: ext4 type with mount point “/”
• Swap partition: swap type with partition size equaling to the size of your physical RAM. If you computer has 16GB RAM, then your swap partition needs to be at least 16GB.
• EFI partition with size about 200MB – 500MB. I use 500MB for my computer

5. Continue the installation. Remember you still need to disable third-party software installation.

If you still get the same error message, then you will need to boot into your BIOS and turn off “Secure Boot”, then follow the above steps to try again.

Let me know if this helped you.

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No matter if you try to install the latest Ubuntu 18.04 LTS, or Linux Mint 19 (based on Ubuntu 18.04 LTS), you may encounter the following error:
GRUB Installation Failed. The ‘grub-efi-amd64-signed’ package failed to install into /target/. Without the GRUB boot loader, the installed system will not boot.

This error is not new and it happens in computers that support UEFI mode, so many people usually recommend to enable the Legacy Support in your BIOS settings to solve this problem. However, based on my experience of dozes of trial-and-errors, I found a simple fix for this error and would like to share with you.

Based on my experiment, I think the culprit of the error is when you allow the installer to install third-party software during the installation, although I don’t know why it causes the error.

So the obvious fix is to leave “Install this third-party software” unchecked when installing Ubuntu, or leave “Install third-party software for graphics and Wi-Fi hardware, Flash, MP3 and other media” unchecked when installing Linux Mint, and you don’t need to enable the Legacy Support in your BIOS settings.

There you have it and I hope it helped you. If it did, please let me know in the comments.