I spend a lot of time working with Amazon’s EC2 (Elastic Compute Cloud) virtual servers. Configuring a new server takes up a surprisingly large amount of time when done manually, and so I use Puppet to automate the process. This works pretty well, but after creating lots of new configuration code I always think it’s worth testing the complete installation on a local Virtual Machine. I’ve built a VM which looks quite a lot like an empty Ubuntu 12.04 cloud image, but have always worried that the CD installation might have a few key differences. Here’s a way to work round some of these.
EC2 instances use a different set of sources for APT, so the first step is to sync these up. Wipe the current /etc/apt/sources.list, and replace with an example from the cloud image you’re trying to emulate. I used the following lines:
deb http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise main deb-src http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise main deb http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise-updates main deb-src http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise-updates main deb http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise universe deb-src http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise universe deb http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise-updates universe deb-src http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ precise-updates universe deb http://security.ubuntu.com/ubuntu precise-security main deb-src http://security.ubuntu.com/ubuntu precise-security main deb http://security.ubuntu.com/ubuntu precise-security universe deb-src http://security.ubuntu.com/ubuntu precise-security universe
Now a quick apt-get update will get you installing the same packages as EC2. The next logical step is to reinstall all the current packages to match. I thought this would be pretty easy, and went for the following invocation:
dpkg --list |
grep ^ii |
awk '{ print($2) }' |
xargs apt-get install --reinstall
This works as follows:
- Get the current list of packages
- Return only those which are actually installed
- Drop everything in the output but the second column (the column containing the package name)
- Pipe into xargs which in turn calls APT.
This got things moving and I’d soon downloaded 397 fresh packages. Unfortunately things then stopped with the (un)helpful message xargs: apt-get: terminated by signal 11. I tried calling APT separately, and got slightly further: Segmentation fault (core dumped). Did I say this got me further?
Reinstalling packages individually seemed to work, so I developed the theory that APT chokes when fed too many packages in one go. This bug seemed to be related. I worked around it with a simple modification to the xargs command to take ten packages at a time:
dpkg --list |
grep ^ii |
awk '{ print($2) }' |
xargs -L 10 apt-get install --reinstall
I decided to take another look at the Launchpad bug report linked earlier. This states:
When trying to –reinstall multiple packages with apt-get, it crashes with a segmentation fault. The command line: apt-get –reinstall install <2-or-more-
packages. ..>
Having used Ubuntu for free for many years I thought it might be about time I gave something back to the community, so I thought I’d take another look. I’ve posted a comment with some more information after getting rather more involved with GDB and apport then I would have liked!
I genuinely don’t know if there is any difference between the packages for EC2 and those in the standard repositories (I rather suspect there isn’t), but if there is then I definitely don’t want to find out about it when trying to fix an urgent problem.