Failed to connect to the hypervisor

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Failed to connect to the hypervisor

There are lots of errors that can occur while connecting to the server (when running virsh for example)

No connection driver available

Symptom

When running a command, the following error (or similar) appears:

$ virsh -c <uri> list
error: no connection driver available for No connection for URI <uri>
error: failed to connect to the hypervisor

Cause

This can happen when libvirt is compiled from sources. The error means there is no driver to use with the specified URI (e.g. "Xen" for "xen://server/")

Investigation

Check the last part of configure ('./configure' or './autogen') output, you should see something like this:

configure: Drivers
configure: 
configure: <driver>: yes

For example talking about Xen:

configure: Drivers
configure: 
configure:     Xen: yes

If however you see "<driver>: no" (e.g. "Xen:no"), that means configure failed to find all the tools/libraries necessary to implement this support or there was "--without-<driver>" parameter specified on the command line.

Solution

Do not specify "--without-<driver>" on the command line of the configuration script and make sure there are all development libraries installed as well, then configure the sources again.

Cannot read CA certificate

Symptom

When running a command, the following error (or similar) appears:

$ virsh -c <uri> list
error: Cannot read CA certificate '/etc/pki/CA/cacert.pem': No such file or directory
error: failed to connect to the hypervisor

Investigation

This error can be caused by various things, for some of them, the error message is little misleading:

  1. specified URI is wrong (missing one '/' -- e.g. 'qemu://system')
  2. connection is not configured

Solution

specified URI is wrong

In the case of specifying 'qemu://system' or 'qemu://session' as a connection URI, virsh is trying to connect to hostname 'system' or 'session' respectively because when hostname is specified, the transport for qemu defaults to 'tls' and thus the need for a certificates. Use three slashes in this case.

connection is not configured

You specified correct URI (e.g. 'qemu[+tls]://server/system') but the certificates were not set up properly on your machine. There is a great In depth guide to configuring TLS. The solution is most probably there.

Permission denied

Symptom

When running a command, the following error (or similar) appears:

$ virsh -c qemu:///system list
error: Failed to connect socket to '/var/run/libvirt/libvirt-sock': Permission denied
error: failed to connect to the hypervisor

Investigation

You are trying to connect using unix socket. The connection to "qemu" without any hostname specified is by default using unix sockets. If there is no error running this command as root it's probably just misconfigured.

Solution

If you want to be able to connect as non-root user using unix sockets, configure following options in '/etc/libvirt/libvirtd.conf' accordingly:

unix_sock_group = <group>
unix_sock_ro_perms = <perms>
unix_sock_rw_perms = <perms>

Other errors

These other errors are even simpler to solve than those mentioned before, so here is a list of error/solutions:

unable to connect to server at 'server:port': Connection refused

The daemon is not running on the server or it's configured not to listen (configuration option 'listen_tcp' or 'listen_tls').

End of file while reading data: nc: using stream socket: Input/output error

If you specified 'ssh' transport, the daemon is probably not running on the server.

End of file while reading data: : Input/output error

If you are using ssh transport, for example, by executing

virsh --connect qemu+ssh://username@remove.host.com/system list

Probably the user you are using to access the server does not belong to the proper group, such as 'libvirtd' for Ubuntu servers. Try adding the user to the proper group on server and connect again. For example, below is to be run on Ubuntu servers.

sudo usermod -G libvirtd -a username

Refer to SSHSetup for setup about other distributions.