Before you attempt to experiment with knockd and/or fwknop, Google around a little for venet0 and packet sniffing.
The virtualization of the interfaces by OpenVZ apparently mangles the IP headers for packet sniffers (like fwknop uses to listen to DROP’d packets). And they then fail to trigger the next step of cleverness (opening the SSH/22 [...]

Fedora 12 maxes out it’s Ruby version at 1.8.6. Unfortunately, compass / sass requires 1.8.7. The following steps creates a suitable RPM, and installs it :

# cd ~
# wget http://mo.morsi.org/blog/files/ruby-1.8.7.249-1.fc11.src_.rpm
# yum install rpm-build
# yum install ncurses-devel gdbm-devel tcl-devel tk-devel libX11-devel  autoconf db4-devel byacc bison emacs compat-readline5-devel
# rpmbuild –rebuild ruby-1.8.7.249-1.fc11.src_.rpm
# cd /root/rpmbuild/RPMS/i386/
# rpm [...]