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1# Imperative Container Management {#sec-imperative-containers}
2
3We'll cover imperative container management using `nixos-container`
4first. Be aware that container management is currently only possible as
5`root`.
6
7You create a container with identifier `foo` as follows:
8
9```ShellSession
10# nixos-container create foo
11```
12
13This creates the container's root directory in `/var/lib/nixos-containers/foo`
14and a small configuration file in `/etc/nixos-containers/foo.conf`. It also
15builds the container's initial system configuration and stores it in
16`/nix/var/nix/profiles/per-container/foo/system`. You can modify the
17initial configuration of the container on the command line. For
18instance, to create a container that has `sshd` running, with the given
19public key for `root`:
20
21```ShellSession
22# nixos-container create foo --config '
23 services.openssh.enable = true;
24 users.users.root.openssh.authorizedKeys.keys = ["ssh-dss AAAAB3N…"];
25'
26```
27
28By default the next free address in the `10.233.0.0/16` subnet will be
29chosen as container IP. This behavior can be altered by setting
30`--host-address` and `--local-address`:
31
32```ShellSession
33# nixos-container create test --config-file test-container.nix \
34 --local-address 10.235.1.2 --host-address 10.235.1.1
35```
36
37Creating a container does not start it. To start the container, run:
38
39```ShellSession
40# nixos-container start foo
41```
42
43This command will return as soon as the container has booted and has
44reached `multi-user.target`. On the host, the container runs within a
45systemd unit called `container@container-name.service`. Thus, if
46something went wrong, you can get status info using `systemctl`:
47
48```ShellSession
49# systemctl status container@foo
50```
51
52If the container has started successfully, you can log in as root using
53the `root-login` operation:
54
55```ShellSession
56# nixos-container root-login foo
57[root@foo:~]#
58```
59
60Note that only root on the host can do this (since there is no
61authentication). You can also get a regular login prompt using the
62`login` operation, which is available to all users on the host:
63
64```ShellSession
65# nixos-container login foo
66foo login: alice
67Password: ***
68```
69
70With `nixos-container run`, you can execute arbitrary commands in the
71container:
72
73```ShellSession
74# nixos-container run foo -- uname -a
75Linux foo 3.4.82 #1-NixOS SMP Thu Mar 20 14:44:05 UTC 2014 x86_64 GNU/Linux
76```
77
78There are several ways to change the configuration of the container.
79First, on the host, you can edit
80`/var/lib/nixos-containers/foo/etc/nixos/configuration.nix`, and run
81
82```ShellSession
83# nixos-container update foo
84```
85
86This will build and activate the new configuration. You can also specify
87a new configuration on the command line:
88
89```ShellSession
90# nixos-container update foo --config '
91 services.httpd.enable = true;
92 services.httpd.adminAddr = "foo@example.org";
93 networking.firewall.allowedTCPPorts = [ 80 ];
94'
95
96# curl http://$(nixos-container show-ip foo)/
97<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">…
98```
99
100However, note that this will overwrite the container's
101`/etc/nixos/configuration.nix`.
102
103Alternatively, you can change the configuration from within the
104container itself by running `nixos-rebuild switch` inside the container.
105Note that the container by default does not have a copy of the NixOS
106channel, so you should run `nix-channel --update` first.
107
108Containers can be stopped and started using `nixos-container
109 stop` and `nixos-container start`, respectively, or by using
110`systemctl` on the container's service unit. To destroy a container,
111including its file system, do
112
113```ShellSession
114# nixos-container destroy foo
115```