Install OMV4 on Debian 9 (Stretch)

cat <<EOF >> /etc/apt/sources.list.d/openmediavault.list
deb http://packages.openmediavault.org/public arrakis main
# deb http://downloads.sourceforge.net/project/openmediavault/packages arrakis main
## Uncomment the following line to add software from the proposed repository.
# deb http://packages.openmediavault.org/public arrakis-proposed main
# deb http://downloads.sourceforge.net/project/openmediavault/packages arrakis-proposed main
## This software is not part of OpenMediaVault, but is offered by third-party
## developers as a service to OpenMediaVault users.
# deb http://packages.openmediavault.org/public arrakis partner
# deb http://downloads.sourceforge.net/project/openmediavault/packages arrakis partner
EOF

export LANG=C.UTF-8
export DEBIAN_FRONTEND=noninteractive
export APT_LISTCHANGES_FRONTEND=none
wget -O "/etc/apt/trusted.gpg.d/openmediavault-archive-keyring.asc" https://packages.openmediavault.org/public/archive.key
apt-key add "/etc/apt/trusted.gpg.d/openmediavault-archive-keyring.asc"
apt-get update
apt-get --yes --auto-remove --show-upgraded \
	--allow-downgrades --allow-change-held-packages \
	--no-install-recommends \
	--option Dpkg::Options::="--force-confdef" \
	--option DPkg::Options::="--force-confold" \
	install postfix openmediavault-keyring openmediavault


# Initialize the system and database.
omv-initsystem


# Rebuild configurations.
omv-mkconf interfaces
omv-mkconf issue


# Display the login information.
cat /etc/issue