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# systemd-nspawn

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systemd-nspawn is like the chroot command, but it is a chroot on steroids.

systemd-nspawn may be used to run a command or OS in a light-weight namespace container. It is more powerful than chroot since it fully virtualizes the file system hierarchy, as well as the process tree, the various IPC subsystems and the host and domain name.

systemd-nspawn limits access to various kernel interfaces in the container to read-only, such as `/sys`, `/proc/sys` or `/sys/fs/selinux`. Network interfaces and the system clock may not be changed from within the container. Device nodes may not be created. The host system cannot be rebooted and kernel modules may not be loaded from within the container.

This mechanism differs from Lxc-systemd or Libvirt-lxc, as it is a much simpler tool to configure.

## Installation

systemd-nspawn is part of and packaged with systemd.

## Examples

### Create and boot a minimal Arch Linux distribution in a container

First install arch-install-scripts.

Next, create a directory to hold the container. In this example we will use `~/MyContainer`.

Next, we use pacstrap to install a basic arch-system into the container. At minimum we need to install the base package.

    # pacstrap -c ~/MyContainer base [additional pkgs/groups]

Tip: The base package does not depend on the linux kernel package and is container-ready.

Once your installation is finished, chroot into the container, and set a root password:

    # systemd-nspawn -D ~/MyContainer
    # passwd
    # logout

Finally, boot into the container:

    # systemd-nspawn -b -D ~/MyContainer

The `-b` option will boot the container (i.e. run `systemd` as PID=1), instead of just running a shell, and `-D` specifies the directory that becomes the container's root directory.

After the container starts, log in as "root" with no password.

Note: If the login fails with "Login incorrect", the problem is likely the `securetty` TTY device whitelist. See #Root login fails.

The container can be powered off by running `poweroff` from within the container. From the host, containers can be controlled by the machinectl tool.

Note: To terminate the session from within the container, hold `Ctrl` and rapidly press `]` three times. Non-US keyboard users should use `%` instead of `]`.

### Create a Debian or Ubuntu environment

Install debootstrap, and one or both of debian-archive-keyring and ubuntu-keyring (obviously install the keyrings for the distros you want).

Note: systemd-nspawn requires that the operating system in the container has systemd running as PID 1 and systemd-nspawn is installed in the container. This means Ubuntu before 15.04 will not work out of the box and requires additional configuration to switch from upstart to systemd. Also make sure that the `systemd-container` package is installed on the container system.

From there it's rather easy to setup Debian or Ubuntu environments:

    # cd /var/lib/machines
    # debootstrap --include=systemd-container --components=main,universe <codename> myContainer <repository-url>

For Debian valid code names are either the rolling names like "stable" and "testing" or release names like "stretch" and "sid", for Ubuntu the code name like "xenial" or "zesty" should be used. A complete list of codenames is in `/usr/share/debootstrap/scripts`. In case of a Debian image the "repository-url" can be `http://deb.debian.org/debian/`. For an Ubuntu image, the "repository-url" can be `http://archive.ubuntu.com/ubuntu/`.

Just like Arch, Debian and Ubuntu will not let you login without a password on first login. To set the root password login without the '-b' option and set a password:

    # systemd-nspawn -D myContainer
    # passwd
    # logout

If the above did not work, one can start the container and use these commands instead:

    # systemd-nspawn -b -D myContainer  #Starts the container
    # machinectl shell root@myContainer /bin/bash  #Get a root bash shell
    # passwd
    # logout

### Creating private users (unprivileged containers)

systemd-nspawn supports unprivileged containers, though the containers need to be booted as root.

Note: This feature requires user_namespaces(7), for further info see Linux Containers#Enable support to run unprivileged containers (optional)

The easiest way to do this is to let systemd-nspawn decide everything:

    # systemd-nspawn -UD myContainer
    # passwd
    # logout
    # systemd-nspawn -bUD myContainer

Here systemd-nspawn will see if the owner of the directory is being used, if not it will use that as base and 65536 IDs above it. On the other hand if the UID/GID is in use it will randomly pick an unused range of 65536 IDs from 524288 - 1878982656 and use them.

Note:

- The base of the range chosen is always a multiple of 65536.
- `-U` and `--private-users=pick` is the same, if kernel supports user namespaces. `--private-users=pick` also implies `--private-users-chown`, see systemd-nspawn(1) for details.

You can also specify the UID/GID of the container manually:

    # systemd-nspawn -D myContainer --private-users=1354956800:65536 --private-users-chown
    # passwd
    # logout
    # systemd-nspawn -bUD myContainer

While booting the container you could still use `--private-users=1354956800:65536` with `--private-users-chown`, but it is unnecessarily complicated, let `-U` handle it after the assigning the IDs.

### Enable container on boot

When using a container frequently, you may want to start it on boot.

First enable the `machines.target` target, then `systemd-nspawn@myContainer.service`, where `myContainer` is an nspawn container in `/var/lib/machines`.

Tip: To customize the startup of a container, edit `/etc/systemd/nspawn/myContainer.nspawn`. See systemd.nspawn(5) for all options.

The container needs to be discoverable by `machinectl`. If it is not in `/var/lib/machines` or in one of the paths searched by `machinectl`, it can be symlinked into `/var/lib/machines` (see machinectl(1)).

A container started with the default template unit file `systemd-nspawn@.service` creates a virtual Ethernet connection (`--network-veth`) which implies a private network (`--private-network`). To retain the default options applied by the `systemd-nspawn` command when no networking options is specified – that is, full access to the host network –, disable the `VirtualEthernet` option:

    /etc/systemd/nspawn/my-container.nspawn

    [Network]
    VirtualEthernet=no

### Build and test packages

See Creating packages for other distributions for example uses.

## Management

### machinectl

This article or section is a candidate for moving to systemd-machined.

Notes: Although machinectl manages systemd-nspawn containers, it is a distinct utility. nspawn containers can be fully managed with machinectl without ever having to manually run the systemd-nspawn command. (Discuss in Talk:Systemd-nspawn#)
Note: The machinectl tool requires systemd and dbus to be installed in the container. See [1] for detailed discussion.

Managing your containers is essentially done with the `machinectl` command. See machinectl(1) for details.

Examples:

Spawn a new shell inside a running container:

    $ machinectl login MyContainer

Show detailed information about a container:

    $ machinectl status MyContainer

Reboot a container:

    $ machinectl reboot MyContainer

Poweroff a container:

    $ machinectl poweroff MyContainer

Tip: Poweroff and reboot operations can be performed from within a container session using the systemctl `poweroff` or `reboot` commands.

Download an image:

    # machinectl pull-tar URL name

### systemd toolchain

Much of the core systemd toolchain has been updated to work with containers. Tools that do usually provide a `-M, --machine=` option which will take a container name as argument.

Examples:

See journal logs for a particular machine:

    $ journalctl -M MyContainer

Show control group contents:

    $ systemd-cgls -M MyContainer

See startup time of container:

    $ systemd-analyze -M MyContainer

For an overview of resource usage:

    $ systemd-cgtop

### Resource control

You can take advantage of control groups to implement limits and resource management of your containers with `systemctl set-property`, see systemd.resource-control(5). For example, you may want to limit the memory amount or CPU usage. To limit the memory consumption of your container to 2 GiB:

    # systemctl set-property systemd-nspawn@myContainer.service MemoryMax=2G

Or to limit the CPU time usage to roughly the equivalent of 2 cores:

    # systemctl set-property systemd-nspawn@myContainer.service CPUQuota=200%

This will create permanent files in `/etc/systemd/system.control/systemd-nspawn@myContainer.service.d/`.

According to the documentation, `MemoryHigh` is the preferred method to keep in check memory consumption, but it will not be hard-limited as is the case with `MemoryMax`. You can use both options leaving `MemoryMax` as the last line of defense. Also take in consideration that you will not limit the number of CPUs the container can see, but you will achieve similar results by limiting how much time the container will get at maximum, relative to the total CPU time.

Tip: If you do not want this changes to be preserved after reboot you can pass the option `--runtime` to make the changes temporary. You can check their results with `systemd-cgtop`.

## Tips and tricks

### Use an X environment

The factual accuracy of this article or section is disputed.

Reason: The note about the systemd version at the end of this section seems to be obsolete. For me (systemd version 239) X applications also work if `/tmp/.X11-unix` is bound rw. (Discuss in Talk:Systemd-nspawn#/tmp/.X11-unix contents have to be bind-mounted as read-only - still relevant?)

See Xhost and Change root#Run graphical applications from chroot.

You will need to set the `DISPLAY` environment variable inside your container session to connect to the external X server.

X stores some required files in the `/tmp` directory. In order for your container to display anything, it needs access to those files. To do so, append the `--bind-ro=/tmp/.X11-unix` option when starting the container.

Note: Since systemd version 235, `/tmp/.X11-unix` contents have to be bind-mounted as read-only, otherwise they will disappear from the filesystem. The read-only mount flag does not prevent using `connect()` syscall on the socket. If you binded also `/run/user/1000` then you might want to explicitly bind `/run/user/1000/bus` as read-only to protect the dbus socket from being deleted.

#### Avoiding xhost

`xhost` only provides rather coarse access rights to the X server. More fine-grained access control is possible via the `$XAUTHORITY` file. Unfortunately, just making the `$XAUTHORITY` file accessible in the container will not do the job: your `$XAUTHORITY` file is specific to your host, but the container is a different host. The following trick adapted from stackoverflow can be used to make your X server accept the `$XAUTHORITY` file from an X application run inside the container:

    $ XAUTH=/tmp/container_xauth
    $ xauth nextract - "$DISPLAY" | sed -e 's/^..../ffff/' | xauth -f "$XAUTH" nmerge -
    # systemd-nspawn -D myContainer --bind=/tmp/.X11-unix --bind="$XAUTH" -E DISPLAY="$DISPLAY" -E XAUTHORITY="$XAUTH" --as-pid2 /usr/bin/xeyes

The second line above sets the connection family to "FamilyWild", value `65535`, which causes the entry to match every display. See Xsecurity(7) for more information.

### Run Firefox

See Firefox tweaks.

### Access host filesystem

See `--bind` and `--bind-ro` in systemd-nspawn(1).

If both the host and the container are Arch Linux, then one could, for example, share the pacman cache:

    # systemd-nspawn --bind=/var/cache/pacman/pkg

Or you can specify per-container bind using the file:

    /etc/systemd/nspawn/my-container.nspawn

    [Files]
    Bind=/var/cache/pacman/pkg

See #Specify per-container settings.

To bind the directory to a different path within the container, add the path be separated by a colon. For example:

    # systemd-nspawn --bind=/path/to/host_dir:/path/to/container_dir

### Configure networking

This article or section needs language, wiki syntax or style improvements. See Help:Style for reference.

Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:Systemd-nspawn#)

For the most simple setup, allowing outgoing connections to the internet, you can use systemd-networkd for network management and DHCP and systemd-resolved for DNS.

This assumes you have started `systemd-nspawn` with the `-n` switch, creating a virtual Ethernet link to the host.

Instead of using systemd-resolved you can also manually edit your container's `/etc/resolv.conf` by adding your DNS server's IP address.

Note the canonical systemd-networkd host and container .network files are from https://github.com/systemd/systemd/tree/master/network .

See systemd-networkd#Usage with containers for more complex examples.

#### Use host networking

To disable private networking used by containers started with `machinectl start MyContainer` add a `MyContainer.nspawn` file to the`/etc/systemd/nspawn` directory (create the directory if needed) and add the following:

    /etc/systemd/nspawn/MyContainer.nspawn

    [Network]
    VirtualEthernet=no

Parameters set in the `MyContainer.nspawn` file will override the defaults used in `systemd-nspawn@.service` and the newly started containers will use the host's networking.

#### Virtual Ethernet interfaces

If a container is started with `systemd-nspawn ... -n`, systemd will automatically create one virtual Ethernet interface on the host, and one in the container, connected by a virtual Ethernet cable.

If the name of the container is `foo`, the name of the virtual Ethernet interface on the host is `ve-foo`. The name of the virtual Ethernet interface in the container is always `host0`.

When examining the interfaces with `ip link`, interface names will be shown with a suffix, such as `ve-foo@if2` and `host0@if9`. The `@ifN` is not actually part of the name of the interface; instead, `ip link` appends this information to indicate which "slot" the virtual Ethernet cable connects to on the other end.

For example, a host virtual Ethernet interface shown as `ve-foo@if2` will connect to container `foo`, and inside the container to the second network interface -- the one shown with index 2 when running `ip link` inside the container. Similarly, in the container, the interface named `host0@if9` will connect to the 9th slot on the host.

Note: If you use a firewall, the traffic of your virtual interface can be blocked as result. You will have to enable the necesary rules to by-pass your firewall.

#### Use a network bridge

If you have configured a network bridge on the host system in order to have an IP address assigned to the container as if it was a physical machine in your local network (see, for example, systemd-networkd#DHCP with two distinct IP or systemd-networkd#Static IP network) you can make systemd-nspawn use it by using the option `--network-bridge=br0`.

### Run on a non-systemd system

See Init#systemd-nspawn.

### Specify per-container settings

To specify per-container settings and not overrides for all (e.g. bind a directory to only one container), the .nspawn files can be used. See systemd.nspawn(5) for details.

### Use Btrfs subvolume as container root

To use a Btrfs subvolume as a template for the container's root, use the `--template` flag. This takes a snapshot of the subvolume and populates the root directory for the container with it.

Note: If the template path specified is not the root of a subvolume, the entire tree is copied. This will be very time consuming.

For example, to use a snapshot located at `/.snapshots/403/snapshot`:

    # systemd-nspawn --template=/.snapshots/403/snapshots -b -D my-container

where `my-container` is the name of the directory that will be created for the container. After powering off, the newly created subvolume is retained.

### Use temporary Btrfs snapshot of container

One can use the `--ephemeral` or `-x` flag to create a temporary btrfs snapshot of the container and use it as the container root. Any changes made while booted in the container will be lost. For example:

    # systemd-nspawn -D my-container -xb

where my-container is the directory of an existing container or system. For example, if `/` is a btrfs subvolume one could create an ephemeral container of the currently running host system by doing:

    # systemd-nspawn -D / -xb

After powering off the container, the btrfs subvolume that was created is immediately removed.

### Run docker in systemd-nspawn

Docker requires `rw` permission of `/sys/fs/cgroup` to run its containers, which is mounted read-only by `systemd-nspawn` by default due to cgroup namespace. However, it is possible to run Docker in a systemd-nspawn container by bind-mounting `/sys/fs/cgroup` from host os and enabling necessary capabilities and permissions.

Note: The following steps are essentially sharing the cgroup namespace to the container, giving kernel keyring permissions and making it a privileged container, which is likely to increase the attack surface and decrease security level. You should always evaluate the actual benefits by doing so before following the steps.

First, cgroup namespace should be disabled by `systemctl edit systemd-nspawn@myContainer`

    systemctl edit systemd-nspawn@myContainer

    [Service]
    Environment=SYSTEMD_NSPAWN_USE_CGNS=0

Then, edit `/etc/systemd/nspawn/myContainer.nspawn` (create if absent) and add the following configurations.

    /etc/systemd/nspawn/myContainer.nspawn

    [Exec]
    Capability=all
    SystemCallFilter=add_key keyctl

    [Files]
    Bind=/sys/fs/cgroup

This grants all capabilities to the container, whitelists two system calls `add_key` and `keyctl` (related to kernel keyring and required by Docker), and bind-mounts `/sys/fs/cgroup` from host to the container. After editing these files, you need to poweroff and restart your container for them to take effect.

Note: You might need to load the `overlay` module on the host before starting Docker inside the systemd-nspawn to use the `overlay2` storage driver (default storage driver of Docker) properly. Failure to load the driver will cause Docker to choose the inefficient driver `vfs` which copies everything for every layer of Docker containers. Consult Kernel modules#Automatic module loading with systemd on how to load the module automatically.

### Using machinectl without root permissions

machined is Polkit enabled, this allows the creation of polkit rules to allow certain actions to be performed without becoming the root user. The different permissions are described in `/usr/share/polkit-1/actions/org.freedesktop.machine1.policy` and all live underneath `org.freedesktop.machine1.`.

To allow a user named "foo" to perform all actions without root permissions, add a policy:

    /etc/polkit-1/rules.d/machined.rules

    polkit.addRule(
      function(action, subject) {
        if (action.id.startsWith("org.freedesktop.machine1.") && subject.user == "foo") {
          return polkit.Result.YES;
        }
      }
    );

Additionally, the user will require permissions to manage the `systemd-nspawn@` units to be able to start and stop nspawn containers, add this policy to allow this:

    /etc/polkit-1/rules.d/machined.rules

    polkit.addRule(
      function(action, subject) {
        if ((action.id.startsWith("org.freedesktop.machine1.") || (action.id == "org.freedesktop.systemd1.manage-units" && action.lookup("unit").startsWith("systemd-nspawn@"))) && subject.user == "foo") {
          return polkit.Result.YES;
        }
      }
    );

## Troubleshooting

### Root login fails

If you get the following error when you try to login (i.e. using `machinectl login <name>`):

    arch-nspawn login: root
    Login incorrect

And `journalctl` shows:

    pam_securetty(login:auth): access denied: tty 'pts/0' is not secure !

Delete `/etc/securetty`[2] and `/usr/share/factory/etc/securetty` on the container file system. Optionally add them to NoExtract in `/etc/pacman.conf` to prevent them from getting reinstalled. See FS#45903 for details.

### Unable to upgrade some packages on the container

It can sometimes be impossible to upgrade some packages on the container, filesystem being a perfect example. The issue is due to `/sys` being mounted as Read Only. The workaround is to remount the directory in Read Write when running `mount -o remount,rw -t sysfs sysfs /sys`, do the upgrade then reboot the container.

### execv(...) failed: Permission denied

When trying to boot the container via `systemd-nspawn -bD /path/to/container` (or executing something in the container), and the following error comes up:

    execv(/usr/lib/systemd/systemd, /lib/systemd/systemd, /sbin/init) failed: Permission denied

even though the permissions of the files in question (i.e. `/lib/systemd/systemd`) are correct, this can be the result of having mounted the file system on which the container is stored as non-root user. For example, if you mount your disk manually with an entry in fstab that has the options `noauto,user,...`, systemd-nspawn will not allow executing the files even if they are owned by root.

### Reboot not working

When trying to reboot the container via machinectl or within the container, the container does not reboot.

Workaround: edit `/usr/lib/systemd/system/systemd-nspawn@.service` and remove `--keep-unit`

Reference: https://github.com/systemd/systemd/issues/2809

### Terminal type in TERM is incorrect (broken colors)

When logging into the container via `machinectl login`, the colors and keystrokes in the terminal within the container might be broken. This may be due to an incorrect terminal type in `TERM` environment variable. The environment variable is not inherited from the shell on the host, but falls back to a default fixed in systemd (`vt220`), unless explicitly configured. To configure, within the container create a configuration overlay for the `container-getty@.service` systemd service that launches the login getty for `machinectl login`, and set `TERM` to the value that matches the host terminal you are logging in from:

    /etc/systemd/system/container-getty@.service.d/term.conf

    [Service]
    Environment=TERM=xterm-256color

Alternatively use `machinectl shell`. It properly inherits the `TERM` environment variable from the terminal.

### Mounting a NFS share inside the container

Not possible at this time (June 2019).

## See also

- Automatic console login
- machinectl man page
- systemd-nspawn man page
- Creating containers with systemd-nspawn
- Presentation by Lennart Pottering on systemd-nspawn
- Running Firefox in a systemd-nspawn container
- Graphical applications in systemd-nspawn

Categories:

- Virtualization
- Sandboxing

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