When running Fedora as a KVM/Qemu host for virtual machines, you have the issue that you don’t know the IP Address for a virtual machine once you create it. IP addresses that are assigned via
The MAC Address is in the config file saved in
/etc/libvirt/qemu/$VMNAME.xml
Once you start the virtual machine, you can fetch the IP Address from the DHCP lease file in:
/var/lib/dnsmasq/dnsmasq.leases
To correlate the two:
#!/bin/bash
VMNAME=$1
MAC=`cat /etc/libvirt/qemu/$VMNAME.xml | xml2 | awk 'BEGIN{FS="="} /mac..address/ {print $2}'`
IP=`grep $MAC /var/lib/dnsmasq/dnsmasq.leases | cut -d' ' -f3`
#$VMNAME has MAC $MAC and IPAddress $IP
echo $IP
This must be called as root or via sudo.
UPDATE:
Chris Lalancette notes that the cannonical version of the MAC address can be found using
virsh -c qemu:///system dumpxml $VMNAME
The dnsmasq process will be listening on libvirt’s network interface, so as long as your VMs all send DHCP_HOSTNAME, you can just query it directly (no root required):
dig +short @192.168.122.1 $VMNAME
I think that leads to a Chicken/Egg problem. For a local VM, the DNS is managed by DNS masq, which reads from /etc/hosts. You don’t know what IP Address to put into /ect/hosts since it is served out of DHCP.
The VMs don’t seem to be sending DHCP_HOSTNAME, but that might be possible to setup in a config option prior to launching the VM.
I meant that dnsmasq will also resolve names from it’s own DHCP leases, so you don’t really need to add anything to /etc/hosts (unless that’s the goal of your exercise…)
It looks like I can get it working by modifying the file
/etc/dhclient-eth0.conf
send fqdn.fqdn “ipa-server-3.ayoung.boston.devel.redhat.com.”;
send fqdn.encoded on;
send fqdn.server-update off;
also request fqdn, dhcp6.fqdn;
Since I already modify this file for the resolve.conf changes, I don’t think this is a problem. If that works, It will be a much better solution. Thanks, Josh. I’ll update when I can test if this works.
There are actually a number of techniques. I find the easiest way is to just run /sbin/arp -an, but you can also look here:
https://rwmj.wordpress.com/2011/03/31/tip-code-for-getting-dhcp-address-from-a-virtual-machine-disk-image/
(In case it wasn’t clear, the two “previously” links from that link as well)
Adam,
I noticed somewhere (may be in one of Rich’s posts) that you could use the below command on the host to get the IP of your guest.
#virt-cat Fedora15tbox /var/log/messages | grep ‘dhclient.*bound to’