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Gentoo Nspawn Container on Ubuntu 17.04 on Digital Ocean.

Install a Gentoo nspawn Container on Ubuntu 17.04 on Digital Ocean.

Spin up an Ubuntu 17.04 droplet, because nspawn containers are slightly more difficult with Ubuntu 16.04. Install systemd-container. (This will also work on your local workstation or laptop running Ubuntu 17.04.)

apt install systemd-container

After installing systemd-container you will discover a new directory, /var/lib/machines, and you can create a directory there for a new container. You'll need a systemd stage3 tarball for gentoo and you can get those from the Gentoo Website

After checking the hash you can extract it to your new folder

cd /var/lib/machines/gentoocontainer/
tar xvjpf /path/to/stage3-*.tar.bz2 --xattrs --numeric-owner
cd ../

Start the container so you can create a root password

systemd-nspawn -D gentoocontainer

Because of how Digital Ocean and Ubuntu set up networking, if you want to subnet the container, start systemd-network (systemd-resolved is probably already running). And optionally it's also pretty straightforward to create a /usr/portage directory on the host operating system, and then bind that directory to the container.

# start the container and login as root
systemd-nspawn -b -D gentoocontainer
# to subnet the container
# start systemd-networkd on host
# and add -n flag
systemctl start systemd-networkd
systemd-nspawn -b -D gentoocontainer -n
# to bind /usr/portage
# create /usr/portage on host
mkdir /usr/portage
# and add the --bind option
systemd-nspawn -b -D gentoocontainer -n --bind=/usr/portage

You should have a root command line on the container, and there really are only two further things to consider: the container probably inherits timezone from the host, but not locale. And your MAKEOPTS="-j", some things seem to not compile if your MAKEOPTS j number is more than the number of cores on the host.

Testing this on a local machine, the nspawn container does not inherit the correct time-zone, so from the container's command line

timedatectl set-timezone <some/time_zone>

And here is what the Gentoo wiki has to say about setting the locale if you're concerned about that, again from the container's command line.

Your systemd-nspawn command will open up one root console, but if you use a multi-plexer like byobu you can run additional sessions with machinectl commands

# also works with new users in the container which you might create
machinectl shell root@gentoocontainer
# and then to get the whole environment call bash
# to power down the container

Before you can install anything, you'll need to update your portage tree, and emerge-webrsync takes care of that easily enough.

If you want to update everything: emerge -avDuN @world

By default, any overlays will end up in /var/lib/layman.
If you need to build mono, it needs a kernel config. Depending on the host operating system you might be able to find one at /proc/config.gz, or in the /boot directory.
If you find yourself fetching git repos repeatedly, you can add EVCS_OFFLINE=1 temporarily in make.conf, and any ebuild that depends on git-r3.eclass will stop fetching from git.

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