pyrox.dev
1# Running Tests interactively {#sec-running-nixos-tests-interactively}
2
3The test itself can be run interactively. This is particularly useful
4when developing or debugging a test:
5
6```ShellSession
7$ nix-build . -A nixosTests.login.driverInteractive
8$ ./result/bin/nixos-test-driver
9[...]
10>>>
11```
12
13::: {.note}
14By executing the test driver in this way,
15the VMs executed may gain network & Internet access via their backdoor control interface,
16typically recognized as `eth0`.
17:::
18
19You can then take any Python statement, e.g.
20
21```py
22>>> start_all()
23>>> test_script()
24>>> machine.succeed("touch /tmp/foo")
25>>> print(machine.succeed("pwd")) # Show stdout of command
26```
27
28The function `test_script` executes the entire test script and drops you
29back into the test driver command line upon its completion. This allows
30you to inspect the state of the VMs after the test (e.g. to debug the
31test script).
32
33## Shell access in interactive mode {#sec-nixos-test-shell-access}
34
35The function `<yourmachine>.shell_interact()` grants access to a shell running
36inside a virtual machine. To use it, replace `<yourmachine>` with the name of a
37virtual machine defined in the test, for example: `machine.shell_interact()`.
38Keep in mind that this shell may not display everything correctly as it is
39running within an interactive Python REPL, and logging output from the virtual
40machine may overwrite input and output from the guest shell:
41
42```py
43>>> machine.shell_interact()
44machine: Terminal is ready (there is no initial prompt):
45$ hostname
46machine
47```
48
49As an alternative, you can proxy the guest shell to a local TCP server by first
50starting a TCP server in a terminal using the command:
51
52```ShellSession
53$ socat 'READLINE,PROMPT=$ ' tcp-listen:4444,reuseaddr
54```
55
56In the terminal where the test driver is running, connect to this server by
57using:
58
59```py
60>>> machine.shell_interact("tcp:127.0.0.1:4444")
61```
62
63Once the connection is established, you can enter commands in the socat terminal
64where socat is running.
65
66## SSH Access for test machines {#sec-nixos-test-ssh-access}
67
68An SSH-based backdoor to log into machines can be enabled with
69
70```nix
71{
72 name = "…";
73 nodes.machines = { /* … */ };
74 interactive.sshBackdoor.enable = true;
75}
76```
77
78::: {.warning}
79Make sure to only enable the backdoor for interactive tests
80(i.e. by using `interactive.sshBackdoor.enable`)! This is the only
81supported configuration.
82
83Running a test in a sandbox with this will fail because `/dev/vhost-vsock` isn't available
84in the sandbox.
85:::
86
87This creates a [vsock socket](https://man7.org/linux/man-pages/man7/vsock.7.html)
88for each VM to log in with SSH. This configures root login with an empty password.
89
90When the VMs get started interactively with the test-driver, it's possible to
91connect to `machine` with
92
93```
94$ ssh vsock/3 -o User=root
95```
96
97The socket numbers correspond to the node number of the test VM, but start
98at three instead of one because that's the lowest possible
99vsock number. The exact SSH commands are also printed out when starting
100`nixos-test-driver`.
101
102On non-NixOS systems you'll probably need to enable
103the SSH config from {manpage}`systemd-ssh-proxy(1)` yourself.
104
105If starting VM fails with an error like
106
107```
108qemu-system-x86_64: -device vhost-vsock-pci,guest-cid=3: vhost-vsock: unable to set guest cid: Address already in use
109```
110
111it means that the vsock numbers for the VMs are already in use. This can happen
112if another interactive test with SSH backdoor enabled is running on the machine.
113
114In that case, you need to assign another range of vsock numbers. You can pick another
115offset with
116
117```nix
118{
119 sshBackdoor = {
120 enable = true;
121 vsockOffset = 23542;
122 };
123}
124```
125
126## Port forwarding to NixOS test VMs {#sec-nixos-test-port-forwarding}
127
128If your test has only a single VM, you may use e.g.
129
130```ShellSession
131$ QEMU_NET_OPTS="hostfwd=tcp:127.0.0.1:2222-:22" ./result/bin/nixos-test-driver
132```
133
134to port-forward a port in the VM (here `22`) to the host machine (here port `2222`).
135
136This naturally does not work when multiple machines are involved,
137since a single port on the host cannot forward to multiple VMs.
138
139If the test defines multiple machines, you may opt to _temporarily_ set
140`virtualisation.forwardPorts` in the test definition for debugging.
141
142Such port forwardings connect via the VM's virtual network interface.
143Thus they cannot connect to ports that are only bound to the VM's
144loopback interface (`127.0.0.1`), and the VM's NixOS firewall
145must be configured to allow these connections.
146
147## Reuse VM state {#sec-nixos-test-reuse-vm-state}
148
149You can re-use the VM states coming from a previous run by setting the
150`--keep-vm-state` flag.
151
152```ShellSession
153$ ./result/bin/nixos-test-driver --keep-vm-state
154```
155
156The machine state is stored in the `$TMPDIR/vm-state-machinename`
157directory.
158
159## Interactive-only test configuration {#sec-nixos-test-interactive-configuration}
160
161The `.driverInteractive` attribute combines the regular test configuration with
162definitions from the [`interactive` submodule](#test-opt-interactive). This gives you
163a more usable, graphical, but slightly different configuration.
164
165You can add your own interactive-only test configuration by adding extra
166configuration to the [`interactive` submodule](#test-opt-interactive).
167
168To interactively run only the regular configuration, build the `<test>.driver` attribute
169instead, and call it with the flag `result/bin/nixos-test-driver --interactive`.