# Imperative Container Management

We’ll cover imperative container management using `nixos-container` first. You create a container with identifier `foo` as follows:

    $ nixos-container create foo

This creates the container’s root directory in `/var/lib/containers/foo` and a small configuration file in `/etc/containers/foo.conf`. It also builds the container’s initial system configuration and stores it in `/nix/var/nix/profiles/per-container/foo/system`. You can modify the initial configuration of the container on the command line. For instance, to create a container that has `sshd` running, with the given public key for `root`:

    $ nixos-container create foo --config 'services.openssh.enable = true; \
      users.extraUsers.root.openssh.authorizedKeys.keys = ["ssh-dss AAAAB3N…"];'

Creating a container does not start it. To start the container, run:

    $ nixos-container start foo

This command will return as soon as the container has booted and has reached `multi-user.target`. On the host, the container runs within a systemd unit called `container@container-name.service`. Thus, if something went wrong, you can get status info using `systemctl`:

    $ systemctl status container@foo

If the container has started succesfully, you can log in as root using the `root-login` operation:

    $ nixos-container root-login foo
    [root@foo:~]#

Note that only root on the host can do this (since there is no authentication). You can also get a regular login prompt using the `login` operation, which is available to all users on the host:

    $ nixos-container login foo
    foo login: alice
    Password: ***

With `nixos-container run`, you can execute arbitrary commands in the container:

    $ nixos-container run foo -- uname -a
    Linux foo 3.4.82 #1-NixOS SMP Thu Mar 20 14:44:05 UTC 2014 x86_64 GNU/Linux

There are several ways to change the configuration of the container. First, on the host, you can edit `/var/lib/container/name/etc/nixos/configuration.nix`, and run

    $ nixos-container update foo

This will build and activate the new configuration. You can also specify a new configuration on the command line:

    $ nixos-container update foo --config 'services.httpd.enable = true; \
      services.httpd.adminAddr = "foo@example.org";'

    $ curl http://$(nixos-container show-ip foo)/
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">…

However, note that this will overwrite the container’s `/etc/nixos/configuration.nix`.

Alternatively, you can change the configuration from within the container itself by running `nixos-rebuild switch` inside the container. Note that the container by default does not have a copy of the NixOS channel, so you should run `nix-channel --update` first.

Containers can be stopped and started using `nixos-container stop` and `nixos-container start`, respectively, or by using `systemctl` on the container’s service unit. To destroy a container, including its file system, do

    $ nixos-container destroy foo