There are various log files stored on the host system to assist with debugging KVM related problems. In this tutorial, I will cover log file locations and tools used to track down KVM problems.

The files are as follows:

Adblock detected 😱

My website is made possible by displaying online advertisements to my visitors. I get it! Ads are annoying but they help keep this website running. It is hard to keep the site running and producing new content when so many people block ads. Please consider donating money to the nixCraft via PayPal/Bitcoin, or become a supporter using Patreon.

1. $HOME/.virtinst/virt-install.log – virt-install tool log file.
2. $HOME/.virt-manager/virt-manager.log – virt-manager tool log file.
3. /var/log/libvirt/qemu/ – Log files for each running virtual machine. If centos is virtual machine name, than log file is /var/log/libvirt/qemu/centos.log.

You can use the grep and other Linux tools to view this files:
# tail -f /var/log/libvirt/qemu/freebsd.log
# grep something $HOME/.virtinst/virt-install.log
$ sudo tail -f /var/log/libvirt/qemu/openbsd.log
Sample outputs:

2016-11-08 17:14:46.909+0000: starting up libvirt version: 1.3.1, package: 1ubuntu10.5 (Stefan Bader <stefan.bader@canonical.com> Thu, 06 Oct 2016 13:07:20 +0200), qemu version: 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.5), hostname: server1.cyberciti.biz
....
.....
..
=29,id=hostnet1,vhost=on,vhostfd=30 -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:8f:31:5f,bus=pci.0,addr=0x4 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -vnc 127.0.0.1:1 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x7 -msg timestamp=on
char device redirected to /dev/pts/8 (label charserial0)

Connecting To Console

Use the virsh command to connect to guest serial console as follows :
$ virsh list
$ virsh console freebsd
This is useful to troubleshoot problem such as networking and much more from host itself. However, you need to configure guest operating system for a serial console. See how to setup a serial console for FreeBSD and CentOS virtual machines.

KVM Configuration Files

You can edit configuration file to define hardware properties for VMs or other setup. They are located in /etc/libvirt/qemu/ directory. Here is sample FreeBSD guest configuration file.
# less /etc/libvirt/qemu/freebsd.xml
OR
$ virsh dumpxml freebsd
Sample outputs:

When you create guests with the virt-manager or virt-install, the guests configuration files are created automatically in the /etc/libvirt/qemu/ directory. You can use this file error checking. You can edit this file using a text editor or virsh command itself:
virsh edit freebsd
virsh edit centos

KVM tools

Type the following command to install kvm-tools package which contains some diagnostics and debugging tools for KVM, such as kvmtrace and kvm_stat, enter:
# yum -y install kvm_tools
You need to mount debugfs, enter:
# mount -t debugfs debugfs /sys/kernel/debug
# kvm_stat
Sample outputs:

You can use normal tools to troubleshoot and get other information using the following tools:

• ps, pstree, and top
• vmstat, iostat, and lsof
• tcpdump, brctl, ip, and ifconfig