I use qemu to virtualize appliances on my servers, and I access them over SSH. Allthough SSH supports streaming X windows so it is possible to fire up a graphical install, it is not so convenient as the connection may drop and cancel the install.

A convenient workaround is to use qemu’s curses interface, where instead of a display, a terminal is attached to the virtual machine. That way you can install and use your virtual machines directly in the SSH terminal.

To install a new system from scratch, simply define the -hda, -cdrom and -boot flags, and add the -curses option:
qemu-system-x86_64  -hda /dev/sdc1 -m 1500 --enable-kvm -curses -cdrom images/debian-stable.iso -boot d

The Debian installer supports headless mode, but we have to add two settings at the boot prompt to make it work with curses.

1. Fire up qemu with the command above. Wait a few seconds, the screen will turn black after loading syslinux. Hit ESC, and enter:
install fb=none vga=normal

and follow the install. Voilà, you’re installing your VM in qemu directly over ssh.

Tip: To prevent losing the install if the network connection is lost, run the commands in a screen terminal.

Recently I was deploying a service that made use of Linux’s IPTABLES feature, but this time in an LXC container. LXC containers provide an extremely lightweight virtualization technology and a simple way to separate environments.

When loading IPTABLES rules in the container I encountered the following error:

This was due to the fact that on the host, the ip6table_filter module was not loaded. Usually, the iptables command will by itself load the module when needed, but LXC shares the kernel of the host system and a container is restricted from loading modules into the host’s kernel.

The solution is to simply load the kernel module on the host:

After that the container will be able to make use of the new kernel module.