Written by Rainer Gerhards (2009-07-15)
The changes introduced in rsyslog v5 are numerous, but not very intrusive. This document describes things to keep in mind when moving from v4 to v5. It does not list enhancements nor does it talk about compatibility concerns introduced by earlier versions (for this, see their respective compatibility documents).
The $HUPisRestart directive is supported by some early v5 versions, but will soon been removed (around 5.1.x). That means that restart-type HUP processing is no longer available. This processing was redundant and had a lot a drawbacks. For details, please see the rsyslog v4 compatibility notes which elaborate on the reasons and the (few) things you may need to change.