## 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.)

```bash
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](http://distfiles.gentoo.org/releases/amd64/autobuilds/current-stage3-amd64-systemd/)  

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

```bash
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

```bash
systemd-nspawn -D gentoocontainer
passwd
logout
```

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.

```bash
# 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 number>", 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

```bash
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](https://wiki.gentoo.org/wiki/Localization/Guide#Generating_specific_locales),
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

```bash
# 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
bash
# to power down the container
poweroff
```

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.