Installer crashed because grub failed to install?

[yuzisee]

Trying to install on a Macbook4,2

I have rEFInd installed, and the boot detection seems to be fine. It's when I get into the graphical Ubuntu installer that at some point it decides to crash saying grub can't be installed.

I disabled SIP in order to install rEFInd. Created an empty EXT4 sda6 mounted at root, and told the installer to install the bootloader onto sda6. My assumption is that rEFInd can read EXT4 and will see the /boot directory installed there. Is that enough?

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63 [modified: lib/partman/automatically_partition/question usr/share/ubiquity/apt-setup]
ProcVersionSignature: Ubuntu 4.4.0-36.55-generic 4.4.16
Uname: Linux 4.4.0-36-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CasperVersion: 1.376
Date: Wed Jun 28 22:46:42 2017
LiveMediaBuild: wattOS-R10-64bit 16.04 - Release amd64
ProcEnviron:
 TERM=unknown
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UbiquitySyslog:

UpgradeStatus: No upgrade log present (probably fresh install)

[yuzisee (yuzisee)]

>> lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.1 LTS
Release: 16.04
Codename: xenial

[yuzisee (yuzisee)]

>> uname -a
Linux guest 4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

[yuzisee (yuzisee)]

>> cat /var/log/installer/version
ubiquity 2.21.63

[Phillip Susi (psusi)]

"wattOS" is not an official Ubuntu flavor and so is not supported here.