Fooling around a bit more with accessing a VM's serial console from a KVM hypervisor with
virsh console mymachine
I found one thing that doesn't carry over from the host to the VM is the terminal window size, so if you try to use something like
vim through the console connection, it seems to assume a 80x25 or so window, and when
vim exits your console is all screwed up.
It looks like a serial connection doesn't have an out-of-band way of passing that info the way telnet or ssh does, so you have set it manually. You can discover your settings on the host machine with
which should show something like:
on the VM, the same command probably shows
zero rows and columns, no wonder it's confused. Fix it by setting the VM to have the same rows and columns as the host with something like:
stty rows 60 columns 142
and you're in business.
So I've been running Ubuntu 10.04 server virtual machines on a host running KVM as the hypervisor, and thought I should take a look at accessing the VM's console from the host, in case there's a problem with the networking on the VM.
The hosts's VM libvirt definition shows a serial port and console defined with
<serial type='pty'> <source path='/dev/pts/1'/> <target port='0'/> <alias name='serial0'/> </serial> <console type='pty' tty='/dev/pts/1'> <source path='/dev/pts/1'/> <target type='serial' port='0'/> <alias name='serial0'/> </console>
and within the stock Ubuntu 10.04 server VM,
dmesg | grep ttyS0 shows:
[ 0.174722] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A [ 0.175027] 00:05: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
So the virtual hardware is all setup on both ends, but
ps aux | grep ttyS0 doesn't show anything
We need to have a process listening to that port. To do that, create a file named
/etc/init/ttyS0.conf with these contents:
# ttyS0 - getty # # This service maintains a getty on ttyS0 from the point the system is # started until it is shut down again. start on stopped rc RUNLEVEL= stop on runlevel [!2345] respawn exec /sbin/getty -L 38400 ttyS0 xterm-color
and then run
initctl start ttyS0
back in the host machine run
virsh list to find the name or id number of your VM, and then
virsh console <your-vm-name-or-number>
to connect, hit return and you should see a login prompt.
I was playing with creating and cloning Ubuntu virtual machines the other day, and got to the point where I had a nicely setup reference image that I could just copy to fire up additional VMs that would be in a pretty usable state.
There are a few things within a cloned VM that you'd want to change if you were going to keep the new instance around, such as the hostname, SSH host keys, and disk UUIDs. I threw together a simple shell script to take care of these things automatically.
#!/bin/sh # # Updates for cloned Ubuntu VM # # # Some initial settings cloned from the master # ROOT=/dev/vda1 SWAP=/dev/vdb1 LONG_HOSTNAME=ubuntu.local SHORT_HOSTNAME=ubuntu if [ -z $1 ] then echo "Usage: $0 <new-hostname>" exit 1 fi # # Update hostname # shorthost=`echo $1 | cut -d . -f 1` echo $1 >/etc/hostname hostname $1 sed -i -e "s/$LONG_HOSTNAME/$1/g" /etc/hosts sed -i -e "s/$SHORT_HOSTNAME/$shorthost/g" /etc/hosts # # Generate new SSH host keys # rm /etc/ssh/ssh_host_* dpkg-reconfigure openssh-server # # Change root partition UUID # OLD_UUID=`blkid -o value $ROOT | head -n 1` NEW_UUID=`uuidgen` tune2fs -U $NEW_UUID $ROOT sed -i -e "s/$OLD_UUID/$NEW_UUID/g" /etc/fstab /boot/grub/grub.cfg # # Change swap partition UUID # OLD_UUID=`blkid -o value $SWAP | head -n 1` NEW_UUID=`uuidgen` swapoff $SWAP mkswap -U $NEW_UUID $SWAP swapon $SWAP sed -i -e "s/$OLD_UUID/$NEW_UUID/g" /etc/fstab # # Remove udev lines forcing new MAC address to probably show up as eth1 # sed -i -e "/PCI device/d" /etc/udev/rules.d/70-persistent-net.rules sed -i -e "/SUBSYSTEM==/d" /etc/udev/rules.d/70-persistent-net.rules echo "UUID and hostname updated, udev nic lines removed, be sure to reboot"
I'd then run it on the cloned machine with something like
This somewhat particular to my specific master VM, in that it's expecting one disk dedicated to root and one disk dedicated to swap, and the VM was created with
ubuntu.local as the hostname. Hopefully though it'll give some ideas about what to look for and how to script those changes.