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Libvirt error Unable to resolve address name or service not known

This article covers tips to fix 'Libvirt error: Unable to resolve address: name or service not known'. 

QEMU guest migration fails and this error message appears:

# virsh migrate qemu qemu+tcp://192.168.122.12/system error: Unable to resolve address name_of_host service '49155': Name or service not known

Note that the address used for migration data cannot be automatically determined from the address used for connecting to destination libvirtd (for example, from qemu+tcp://192.168.122.12/system). 

This is because to communicate with the destination libvirtd, the source libvirtd may need to use network infrastructure different from that which virsh (possibly running on a separate machine) requires.


To fix Libvirt error: Unable to resolve address: name or service not known:

The best solution is to configure DNS correctly so that all hosts involved in migration are able to resolve all host names.

If DNS cannot be configured to do this, a list of every host used for migration can be added manually to the /etc/hosts file on each of the hosts. 

However, it is difficult to keep such lists consistent in a dynamic environment.

i. If the host names cannot be made resolvable by any means, virsh migrate supports specifying the migration host:

# virsh migrate qemu qemu+tcp://192.168.122.12/system tcp://192.168.122.12

Destination libvirtd will take the tcp://192.168.122.12 URI and append an automatically generated port number. 

ii. If this is not desirable (because of firewall configuration, for example), the port number can be specified in this command:

# virsh migrate qemu qemu+tcp://192.168.122.12/system tcp://192.168.122.12:12345

iii. Another option is to use tunnelled migration. Tunnelled migration does not create a separate connection for migration data, but instead tunnels the data through the connection used for communication with destination libvirtd (for example, qemu+tcp://192.168.122.12/system):

# virsh migrate qemu qemu+tcp://192.168.122.12/system --p2p --tunnelled

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