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 [...]

Quick fix in a container (assuming the host has the correct time :

rm /etc/localtime
ln -s /usr/share/zoneinfo/US/Eastern /etc/localtime

This one is a little embarrassing.
Just trying to install Magento on a new (fresh) container. Running across the following style of error (when executing ./pear install magento-core/Mage_All_Latest-stable) :

Starting to download Lib_ZF_Locale-1.7.2.2.tgz (1,279,370 bytes)
…done: 1,279,370 bytes
install ok: channel://connect.magentocommerce.com/core/Lib_ZF_Locale-1.7.2.2
Notice: Undefined variable: php_errormsg in Installer.php on line 566
PHP Notice:  Undefined variable: php_errormsg in /home/complex/www/magento/downloader/pearlib/php/PEAR/Installer.php on line 566
ERROR: [...]