BTRFS-Install; separate home-partition; dual-boot; grub-efi fails

[Claudius Raphael Paeth]

Ubiquity fails to install Grub on existing ESP (EFI-System-Partition) for Dual-Boot of Ubuntu Bionic 18.04 Release to existing Windows 10 Professional.

Disk is a 320GB HDD SATA, GPT, EFI System Partition and an existing Windows-Partition.

Installed Ubuntu 18.04 for / on BTRFS, plus a separate /home on BTRFS.

Just for the sake of completeness, tried to install Cosmic, Yakkety, Xenial and Trusty in exact same manner and they all do complete.

Reproducible for all variants of Grub-Target-Option, namingly GPT-pMBR, BIOS_GRUB, /efi/boot (ESP), separate /boot (ext-|-2|-3|-4).

Standard and OEM-Install.

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Haven't looked into Ubiquity-Source, but would assume, that between previous (<bionic) and latest (>bionic) something has changed as only bionic fails to replace BOOTX64 (as set before through Windows 10); If BOOTX64 is deleted before install via ubiquity the installer works correctly, identical to cosmic.

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Hope it helps.

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Errors can be found in UbiquitySyslog.txt, going on from:

Nov 29 16:57:18 ubuntu ubiquity: E: Schreiben des Protokolls nicht möglich (Ist /dev/pts eingebunden?) - posix_openpt (19: Kein passendes Gerät gefunden)

Also the final error that leads to Ubiquity breaking:

Nov 29 16:58:11 ubuntu ubiquity: Could not prepare Boot variable: No such file or directory

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ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.6
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CasperVersion: 1.394
CurrentDesktop: ubuntu:GNOME
Date: Thu Nov 29 17:58:47 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper only-ubiquity quiet splash oem-config/enable=true ---
LiveMediaBuild: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
ProcEnviron:
 LANGUAGE=de_DE.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install) #It is a fresh install