Creating a CentOS VM From the CLI...

epretorious

@olivierlambert I'm just wanting to create a CentOS VM using the CLI.

olivierlambert

In an automated fashion? Manually? Provision a VM without any human? Want to repeat that a lot of time or just one shot?

Depending on your final use cases, there's different answers

epretorious

@olivierlambert Thanks for asking! My goal is to manually create a single CentOS VM so that I can get a better understanding all of the complicated details that XO hides from XCP-ng/XenServer administrators.

olivierlambert

It's not rocket science but it's not trivial either Let me give you some details.

For VM creation, all clients are doing (broadly) the same thing behind: cloning a template, passing various configuration and starting the VM. XO is going deeper with Cloudinit support (and other stuff that xe and XenCenter can't achieve since they aren't persistent like XO).

But what matters is this: everything has to go to the XAPI in the end (xe IS a client for XAPI, so if you do things via xe, you are not doing what XO does, since XO is calling XAPI directly, not xe behind!).

So XAPI is the "core" of all those clients: see https://xapi-project.github.io/xen-api/ for an idea on XAPI functions.

xo-server is making a permanent connection to it, and since it's persistent and connected to multiple XAPI (pools) at the same time, can do very cool stuff in terms of orchestration, provisioning, backup and such.

epretorious

@olivierlambert Thanks!

Using only the CLI: How can I connect VNC to the guest in order to complete the installation? e.g., xe console-list vm-name-label=<<<your_vm>>> lists an HTTP URL for connecting to the host...

# xe console-list vm-name-label=CentOS7-1 
uuid ( RO)             : fd376ea3-a644-2ed3-2d72-8ae7ca7a6b71
          vm-uuid ( RO): 2f343ae1-0d57-ef21-6a54-6abe7b7264c6
    vm-name-label ( RO): CentOS7-1
         protocol ( RO): RFB
         location ( RO): https://192.168.0.93/console?uuid=fd376ea3-a644-2ed3-2d72-8ae7ca7a6b71

But it doesn't seem to do anything!

TIA,
Eric P.
Reno, Nevada

olivierlambert

You can't access the VNC directly without authenticating. So you need to point your VNC client to it and enter XAPI creds (IIRC).

epretorious

I think that this wiki page from the Xen Project may provide the answer:

Use SSH to tunnel localhost:5900 to TCP/5900 of the host system. And then
Use a VNC client to access localhost:5900.

I've already confirmed that the host is listening on TCP/5900:

# netstat -tanp | grep \:59
tcp        0      0 127.0.0.1:5900          0.0.0.0:*               LISTEN      1276/vncterm

So I configured the tunnel:

$ ssh -L 5900:localhost:5900 root@192.168.0.92
root@192.168.0.92's password: 
Last login: Tue Nov  1 01:10:30 2022

# xe vm-list name-label=CentOS7-1 
uuid ( RO)           : 2f343ae1-0d57-ef21-6a54-6abe7b7264c6
     name-label ( RW): CentOS7-1
    power-state ( RO): running

# xe vm-list name-label=CentOS7-1 params=dom-id
dom-id ( RO)    : 1

And then I launched the client and connected to localhost:5900:

$ vncviewer 

TigerVNC Viewer 64-bit v1.12.0
Built on: 2022-03-25 17:06
Copyright (C) 1999-2021 TigerVNC Team and many others (see README.rst)
See https://www.tigervnc.org for information on TigerVNC.

Mon Oct 31 18:18:08 2022
 DecodeManager: Detected 8 CPU core(s)
 DecodeManager: Creating 4 decoder thread(s)
 CConn:       Connected to host localhost port 5900
 CConnection: Server supports RFB protocol version 3.3
 CConnection: Using RFB protocol version 3.3
 CConn:       Using pixel format depth 24 (32bpp) little-endian rgb888

A connection is established:

# netstat -tanp | grep \:59
tcp        0      0 127.0.0.1:5900          0.0.0.0:*               LISTEN      1276/vncterm        
tcp        0      0 127.0.0.1:34046         127.0.0.1:5900          ESTABLISHED 18949/sshd: root@pt 
tcp        0      0 127.0.0.1:5900          127.0.0.1:34046         ESTABLISHED 1276/vncterm

But the display seems to be a text console on the host system!

Have I misunderstood some detail?

Eric P.
Reno, Nevada

epretorious

@olivierlambert Yes - I authenticated as the root user. But after that there was nothing - Only a terminal session like a standard SSH session!

Ideas? Suggestions?

Eric P.
Reno, Nevada

epretorious

FWIW: I did notice that there was more than one TCP port connected to the VNC server:

# netstat -tanp | grep vnc
tcp        0      0 127.0.0.1:5900          0.0.0.0:*               LISTEN      1276/vncterm        
tcp        0      0 127.0.0.1:9500          0.0.0.0:*               LISTEN      1276/vncterm

So I also connected to the TCP/9500 port:

$ ssh -L 9500:localhost:9500 root@192.168.0.92
root@192.168.0.92's password: 
Last login: Tue Nov  1 01:14:11 2022

# xe vm-list name-label=CentOS7-1 
uuid ( RO)           : 2f343ae1-0d57-ef21-6a54-6abe7b7264c6
     name-label ( RW): CentOS7-1
    power-state ( RO): running

# xe vm-list name-label=CentOS7-1 params=dom-id
dom-id ( RO)    : 1

But nothing ever happened! i.e., The VNC client failed to open a window on my local system.

What's the purpose of this other VNC daemon on TCP/9500?

TIA,
Eric P.
Reno, Nevada

epretorious

What's the purpose of this other VNC daemon on TCP/9500?

From the Xen Project wiki page on XCP:

The ports used for VNC console are 5901-5999, and the ports used for text console are 9501-9599.

AFAICT: TCP/5900 & TCP/9500 belong to Dom0...

# xenstore-ls /local/domain/0
control = ""
 feature-poweroff = "1"
 feature-reboot = "1"
 feature-suspend = "1"
domid = "0"
name = "Domain-0"
vncterm-pid = "1276"
console = ""
 vnc-port = "5900"
 tc-port = "9500"
vm = "/vm/7a4488c6-d4ac-4aaf-83f0-fb6d3f557f48"

But I don't know how to connect to DomU #1's console because there is no entry in Xenstore for DomU #1:

# xenstore-ls /local/domain/1
xenstore-ls: xs_directory (/local/domain/1): No such file or directory

Ideas? Suggestions?

Eric P.
Reno, Nevada