Start a systemd service inside chroot from a non systemd based rootfs

With init scripts (or with openrc) I alway could run services from a different installation root.
but when I run chroot /somepath/to_root /usr/bin/systemctl start someservice I got:

Running in chroot, ignoring request.

Is there a way to force systemd run the service?

Update:
I forgot to say my host system run init scripts or openrc, but never systemd, and that I use chroot to troubleshot Unix systems which can't even launch a minimal shell.

A well-known problem in systemd distros (Arch Linux, OpenSUSE, Fedora).

Systemd replaces sysvinit, and provides one great advantage over this. In sysvinit, when you ask a service to start, it inherits the execution context of the person invoking the script, which includes environment variables, ulimits, and so on. Systemd improves on this at the contrary by notifying a daemon, which will start the service in a well-defined, healthy, constant environment, where of course the performances of the services are much easier to predict, since the environment is always the same.

This implies that, when I call systemctl from within the chroot, it is irrelevant that I am inside chroot, the environment that will be inherited is still that of PID 1, not my current one. But it gets worse than this: since communication sockets are placed inside /run/systemd, a process in a chroot will not even be able to talk to the init system!

So how do you go about chroot'ing in systemd distros?

1. If all you want to do is have a Linux container, this Arch Wiki page will tell you how to set up a Linux container in less than 30 seconds, thanks to systemd-nspawn.

2. If instead you really want a chroot environment, this beautiful and crystal clear Web page will provide you with two working solutions (the second one is a modified version of the one offered at point #1).

Several years later I must admit there is only one solution to most Systemd practical problems. Because the error is Systemd itself

I am really fed up with Systemd as I had problems that I never faced with things like Upstart or Openrc :

• The enforcing of a kernel requiring cgroups support (instead of being made optional but enabled by default inside a config file) even for embedded systems with only 24Mb of ram and no writable storage.
  While proponents argue that not being able to use it in such case is the wanted behavior since it wasn’t designed for such case, the reality is the other init systems also don’t care while in systemd such feature isn’t a separate project which highlights once again the consequences of not following kiss.
• Despite the claim of being modular, at runtime the dependency hell makes it a strong god object : want to boot over a single reiser4 rootfs ? It’s not possible because many programs requires systemd-udevd which requires systemd-init which requires the systemd-boot package which can’t be installed at the same time than grub2 nor can read kernel images from a reiser4 partition.
• Want to connect to the internet through Bluetooth dialup ? If it doesn’t work with your Samsung java me phone, then you aren’t able to run the scripts and command line software that previously worked manually because of networkd.
• Though I recognize the biggest problem is if you are building and maintaining your own Linux distribution : the systemd init module itself has so many dependencies that you can’t propose to choose another init system through different install packages.
• The default use of Google dns for systemd if no resolver is defined in terms of privacy.
• The inability to launch a background non service process and log out as there are no simple ways to do it in a new systemd scope.
• Good luck for viewing logs if you can’t chroot in your system or if you upgraded from libdb4.8 (whereas at least, in worst case Microsoft has it’s log files in xml format).

The only solution :

Systemd is unnecessary complex for solving problems : like alsa instead of ossv4. So if you have something that uses systemd just wipe all the data :

dd if=/dev/urandom of=/dev/dm−0 bs=1M

and install something that doesn’t use it at all while solving problems of SysV Init like Gentoo with Openrc.
Concerning my question systemd makes things like the Windows® registry : if a part of it gets screwed up, then it’s over.

systemd only ignores "services", so I just run the daemon commands manually.

So instead of

service sshd start

I use

/usr/sbin/sshd -D &

No. Services are executed by systemd (pid 1), not by systemctl directly (which only sends a start request), and since systemd runs outside the chroot, so will the service.

Although technically it could be possible to implement this (by making systemctl somehow pass its root to systemd), it is somewhat unlikely to happen since there already is a tool for creating full containers (systemd-nspawn /somepath/to_root). You could always contact the mailing list though.

Faced this problem once tried to bring up network in rescue mode using network configuration from chroot. Finally this works for me:

service --skip-redirect <service> restart

or:

SYSTEMCTL_SKIP_REDIRECT=_ /etc/init.d/<service> restart