TLS x509 certificate setup

Public Key Infrastructure set up

If you are unsure how to create TLS certificates, skip to the next section.

Location Machine Description Required fields
/etc/pki/CA/cacert.pem Installed on the client and server CA's certificate (more info) n/a
$HOME/.pki/cacert.pem Installed on the client CA's certificate (more info) n/a
/etc/pki/libvirt/private/serverkey.pem Installed on the server Server's private key (more info) n/a
/etc/pki/libvirt/servercert.pem Installed on the server Server's certificate signed by the CA. (more info) CommonName (CN) must be the hostname of the server as it is seen by clients. All hostname and IP address variants that might be used to reach the server should be listed in Subject Alt Name fields.
/etc/pki/libvirt/private/clientkey.pem Installed on the client Client's private key. (more info) n/a
/etc/pki/libvirt/clientcert.pem Installed on the client Client's certificate signed by the CA (more info) Distinguished Name (DN) can be checked against an access control list (tls_allowed_dn_list).
$HOME/.pki/libvirt/clientkey.pem Installed on the client Client's private key. (more info) n/a
$HOME/.pki/libvirt/clientcert.pem Installed on the client Client's certificate signed by the CA (more info) Distinguished Name (DN) can be checked against an access control list (tls_allowed_dn_list).

If 'pkipath' is specified in URI, then all the client certificates must be found in the path specified, otherwise the connection will fail with a fatal error. If 'pkipath' is not specified:

Background to TLS certificates

Libvirt supports TLS certificates for verifying the identity of the server and clients. There are two distinct checks involved:

For full certificate checking you will need to have certificates issued by a recognised Certificate Authority (CA) for your server(s) and all clients. To avoid the expense of getting certificates from a commercial CA, you can set up your own CA and tell your server(s) and clients to trust certificates issues by your own CA. Follow the instructions in the next section.

Be aware that the default configuration for libvirtd allows any client to connect provided they have a valid certificate issued by the CA for their own IP address. You may want to change this to make it less (or more) permissive, depending on your needs.

Setting up a Certificate Authority (CA)

You will need the GnuTLS certtool program documented here. In Fedora, it is in the gnutls-utils package.

Create a private key for your CA:

certtool --generate-privkey > cakey.pem

and self-sign it by creating a file with the signature details called containing:

cn = Name of your organization
certtool --generate-self-signed --load-privkey cakey.pem \
  --template --outfile cacert.pem

(You can delete file now if you want).

Now you have two files which matter:

cacert.pem has to be installed on clients and server(s) to let them know that they can trust certificates issued by your CA.

The normal installation directory for cacert.pem is /etc/pki/CA/cacert.pem on all clients and servers.

To see the contents of this file, do:

certtool -i --infile cacert.pem

X.509 certificate info:

Version: 3
Serial Number (hex): 00
Subject: CN=Libvirt Project
Issuer: CN=Libvirt Project
Signature Algorithm: RSA-SHA
        Not Before: Mon Jun 18 16:22:18 2007
        Not After: Tue Jun 17 16:22:18 2008

This is all that is required to set up your CA. Keep the CA's private key carefully as you will need it when you come to issue certificates for your clients and servers.

Issuing server certificates

For each server (libvirtd) you need to issue a certificate containing one or more hostnames and/or IP addresses. Historically the CommonName (CN) field would contain the hostname of the server and would match the hostname used in the URI that clients pass to libvirt. In most TLS implementations the CN field is considered legacy data. The preferential mechanism is to use Subject Alt Name (SAN) extension fields to validate against. In the future use of the CN field for validation may be discontinued entirely, so it is strongly recommended to include the SAN fields.

In the example below, clients will be connecting to the server using a URI of qemu://, so the CN must be "".

Make a private key for the server:

certtool --generate-privkey > serverkey.pem

and sign that key with the CA's private key by first creating a template file called The template file will contain a number of fields to define the server as follows:

organization = Name of your organization
cn =
dns_name = compute1
dns_name =
ip_address =
ip_address =
ip_address = 2001:cafe::74
ip_address = fe20::24

The 'cn' field should refer to the fully qualified public hostname of the server. For the SAN extension data, there must also be one or more 'dns_name' fields that contain all possible hostnames that can be reasonably used by clients to reach the server, both with and without domain name qualifiers. If clients are likely to connect to the server by IP address, then one or more 'ip_address' fields should also be added.

Use the template file as input to a certtool command to sign the server certificate:

certtool --generate-certificate --load-privkey serverkey.pem \
  --load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
  --template --outfile servercert.pem

This gives two files:

We can examine this certificate and its signature:

certtool -i --infile servercert.pem
X.509 certificate info:

Version: 3
Serial Number (hex): 00
Subject: O=Libvirt Project,
Issuer: CN=Libvirt Project
Signature Algorithm: RSA-SHA
        Not Before: Wed Oct 04 09:09:44 UTC 2017
        Not After: Thu Oct 04 09:09:44 UTC 2018
        Basic Constraints (critical):
                Certificate Authority (CA): FALSE
        Subject Alternative Name (not critical):
                DNSname: compute1
                IPAddress: 2001:cafe::74
                IPAddress: fe20::24

Note the "Issuer" CN is "Libvirt Project" (the CA) and the "Subject" CN is "" (the server). Notice that the hostname listed in the CN must also be duplicated as a DNSname entry

Finally we have two files to install:

Issuing client certificates

For each client (ie. any program linked with libvirt, such as virt-manager) you need to issue a certificate with the X.509 Distinguished Name (DN) set to a suitable name. You can decide this on a company / organisation policy. For example:

C=GB,ST=London,L=London,O=Libvirt Project,CN=name_of_client

The process is the same as for setting up the server certificate so here we just briefly cover the steps.

  1. Make a private key:
    certtool --generate-privkey > clientkey.pem
  2. Act as CA and sign the certificate. Create containing:
    country = GB
    state = London
    locality = London
    organization = Libvirt Project
    cn = client1
    and sign by doing:
    certtool --generate-certificate --load-privkey clientkey.pem \
      --load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
      --template --outfile clientcert.pem
  3. Install the certificates on the client machine:
    cp clientkey.pem /etc/pki/libvirt/private/clientkey.pem
    cp clientcert.pem /etc/pki/libvirt/clientcert.pem

Troubleshooting TLS certificate problems

failed to verify client's certificate

On the server side, run the libvirtd server with the '--listen' and '--verbose' options while the client is connecting. The verbose log messages should tell you enough to diagnose the problem.

You can use the virt-pki-validate shell script to analyze the setup on the client or server machines, preferably as root. It will try to point out the possible problems and provide solutions to fix the set up up to a point where you have secure remote access.