1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
|
=================
Libvirt SSH proxy
=================
Sometimes it's necessary to run some commands inside a guest. While libvirt
already provides a `NSS module <nss.html>`__ that can translate guest name to
IP address it has some limitations (e.g. guest has to have a network interface
plugged into a libvirt-managed network). To resolve some of these limitations,
libvirt offers a SSH proxy. It consists of a SSH client config file
(``/etc/ssh/ssh_config.d/30-libvirt-ssh-proxy.conf``) and a small binary. Both
are automatically installed by ``libvirt-ssh-proxy`` package which is dragged
in by ``libvirt-client``, ``libvirt-daemon-qemu`` and/or ``daemon-kvm`` RPM
packages. After running either of:
::
ssh user@qemu:system/virtualMachine
ssh user@qemu:session/virtualMachine
the configuration file instructs SSH client to start the binary helper which
finds a VSOCK device inside the ``virtualMachine`` and establishes a connection
to it.
For now, only QEMU domains are implemented and the lookup of the
``virtualMachine`` is done under ``qemu:///system`` URI for ``qemu:system`` or
under ``qemu:///session`` URI for ``qemu:session``.
For convenience, there's also another alternative:
::
ssh user@qemu/virtualMachine
where the ``virtualMachine`` is looked up under ``qemu:///system`` first,
possibly followed by ``qemu:///session`` (for cases where ssh client runs as
non-root, since there's no ``qemu:///session`` for root).
Accepted values for ``virtualMachine`` are: domain name (as reported by e.g.
`virsh list`), domain UUID and finally domain ID.
Guest OS requirements
---------------------
It is obvious that the SSH daemon inside the guest needs to be configured to
listen for incoming connections on a VSOCK. There are couple of ways to achieve
this:
* Run systemd-v256 or newer inside the guest.
In this release, systemd started to deploy ``systemd-ssh-generator`` which
should configure socket activation for SSHD automagically.
* Set up socket activation for VSOCK.
We can take an inspiration in the unit file generated by
``systemd-ssh-generator``:
::
[Unit]
Description=OpenSSH Server Socket (systemd-ssh-generator, AF_VSOCK)
Documentation=man:systemd-ssh-generator(8)
Wants=ssh-access.target
Before=ssh-access.target
[Socket]
ListenStream=vsock::22
Accept=yes
PollLimitIntervalSec=30s
PollLimitBurst=50
* Run a service that forwards VSOCK <=> SSHD communication
For instance:
::
socat VSOCK-LISTEN:22,reuseaddr,fork TCP:localhost:22
Libvirt domain XML configuration
--------------------------------
Since the SSH proxy uses a VSOCK to communicate with the SSH daemon running
inside the guest, it is a must to configure VSOCK in the `domain XML
<formatdomain.html#vsock>`__.
|
