Ошибка failed to connect to the hypervisor

Are you receiving the error failed to connect to the hypervisor while running virsh?

The reason for this can vary from no connection driver to missing permissions.

At Bobcares, we often get a request to fix virsh errors, as a part of our Server Management Services.

Today, let’s see why this error occurs and will also see how our Support Engineers fix it.

Virsh error failed to connect to the hypervisor

Virsh is a command-line tool used for managing guest VMs and the hypervisor. But connecting to the server while running virsh can sometimes end up in errors.

And one such error message is ‘error: failed to connect to the hypervisor’. There can be many possible reasons for this error to occur.

Let’s have a look at a few of them.

Causes and fixes for the virsh error

Our customers often approach us with errors while running virsh. Let’s see a few instances where our Support Engineers fixed this error.

1. Connection driver unavailable

While running a virsh command, a user got the following error message.

error: no connection driver available for No connection for URI 
error: failed to connect to the hypervisor

The error message clearly specifies that there is no connection driver for the URI. So our Support Engineers check the configure output. And it should appear as,

configure: Drivers
configure:
configure: : yes

We also check the development libraries and configure the sources if needed.

2. Unable to read CA certificate

Another customer got a different error message while running the virsh command. And the error message was,

error: Cannot read CA certificate '/etc/pki/CA/cacert.pem': No such file or directory
error: failed to connect to the hypervisor

This can be due to two possible reasons – incorrect URI or connection configuration error.

So our Support Engineers check the specified URI and correct it if needed. If the error is with the configuration, then it needs a detailed look. And our Experts check it and fix the error.

3. Permission denied error

Similarly, another error message while running a virsh command is,

error: Failed to connect socket to '/var/run/libvirt/libvirt-sock': Permission denied
error: failed to connect to the hypervisor

Here we check if the same error shows up while running the command as a root user. If the non-root user is only getting this error then the error is with the configuration.

To fix this our Support Engineers edit the /etc/libvirt/libvirt.conf file. And we add the permissions, which appears as,

#unix_sock_group = "libvirt"
#unix_sock_ro_perms = "0777"
#unix_sock_rw_perms = "0770"

Later we restart the libvirtd service. And this fixed the error.

4. Connection refused while running virsh

While trying to connect to a host system the virsh command fails with the error message.

error: failed to connect to the hypervisor
error: unable to connect to the server at 'host:16509': Connection refused

The error message indicates that the libvirt is not listening on the TCP port. So our Support Engineers check the /etc/libvirt/libvirtd.conf file.

And we ensure that the TCP port is listening. We also check if the libvirt configuration is correct or not.

For this, we open the /etc/sysconfig/libvirtd file. Here we uncomment the line,

Later on, restarting the libvirt the error resolves.

5. Authentication failure while connecting to the hypervisor

In addition, some users get auth failed error while connecting to the server using virsh. Here the error message appears as

error: failed to connect to the hypervisor
error: authentication failed: authentication failed

This can be either due to incorrect credentials or else due to improper configuration.

So our Support Engineers check the /etc/libvirt/libvirtd.conf file. And ensure that the auth_tcp value is set to sasl. And we edit the /etc/sasl2/libvirt.conf file and add the following

mech_list: digest-md5
sasldb_path: /etc/libvirt/passwd.db

We also ensure to check the cyrus-sasl-md5 package. Later we restart the libvirt service and set user name and password for SASL.

[Need assistance in fixing virsh errors? – We can help you.]

Conclusion

So far we saw the various reasons for the virsh error failed to connect to the hypervisor. This can be due to driver connection, permissions, etc. Today, we saw how our Support Engineers fix this error.

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@S4nfs, huge thanks for your appreciation of my work. I wish I could spend more time on my projects so that I could finish them and improve them from time to time 😅

Thanks a lot for providing me the full error message. In this case I think you’re right and it’s not something I could test on my side ’cause I’m only relying on the PHP embedded web server to run the web interface.

Regarding the deployment, I got two working deployments using the PHP embedded web server and then just using the script start-web-server.sh to fire it up. So, I got a local deployment and a remote deployment on a small dedicated server. That’s why I didn’t encountered similar issues as you did.

What I don’t understand in your case is why apparently libvirt is trying to write into your apache web folder under a .cache/libvirt subfolder…

Just to make sure that the issue is not in the code / to isolate it correctly, could you please just try running the script start-web-server.sh and see if you get the same issue?

Otherwise, if you can’t, what you can do would be to create that /var/www/.cache folder and set it temporarily to chmod 777 and see under which user the libvirt folder got created. Once done, try to restrict write access to only the related user used to create that libvirt folder.

Also, I don’t think that having deployed everything on the same host would be an issue. Basically if you check the code, I’m simply calling the libvirt binaries like virsh, parsing the output and render it in the web interface. And as I just deployed the code in the $HOME folder, I didn’t had the same permission issues you had.

I’ll try to setup a VM with apache + the nested virtualization enabled and do some tests to understand what caused your issue, debug it and then document my findings + workarounds if possible.

Thanks again for having took the time to report your issue 🙇🏽