Mongrel2 crashes when launched with the -sudo option on Ubuntu (at least up to 11.10).

This has been tracked down to the Ubuntu build of the ZeroMQ library.

The simple solution until the package is fixed is to build ZeroMQ yourself. Apart from the usual build tools that I’m sure you already have running, you may have to add uuid-dev. Anyway configure will tell you.

So, just get the stable tarball over at 0MQ headquaters and compile it the usual way.

wget http://download.zeromq.org/zeromq-2.1.11.tar.gz
tar xzf zeromq-2.1.11.tar.gz
cd zeromq-2.1.11
./configure
make
sudo make install

Also make sure to remove the Ubuntu package because it gets in the way (as it installs in /usr/lib).

Finally for good measure, rebuild your mongrel2:

make clean all
sudo make install