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Installation on my rhel5 laptop was straightforward, as was creating and starting up a VM using the gui application. The only hitch was that redhat4 - actually the Scientific Linux equivalent - did not make a good guest: it failed to boot. SL5 and SL6 guests are ok. The VirtualBox doc warns that kernels which are too old, including the one in rhel4, have problems. In fact, they also discourage use of 2.6.18 (rhel5 and SL5 kernel) in the guest, claiming it suffers from race conditions at boot, but I haven't seen any signs of that.
SDK
Part of the attraction of VirtualBox is the comprehensive API. It turns out this is not part of the standard install; the interface and some sample programs are in a separate platform-independent zip file. Instructions for installations were practically non-existent. Some essential steps (e.g., appropriately defining a couple environment variables) were not mentioned anywhere, but by reading the installation script, etc., I think I figured out what was required and now have a usable installation.
The next step was to try the C++ sample program which
- Connects to the Virtual Box manager (starts it up if not already running)
- Lists virtual machines which are already known to the Manager
- Creates a new VM
There were some hard-coded file paths, etc., which caused 3. to fail. However that step still failed even after I fixed them (all the ones I'm aware of, anyway). At least it fails further along in the process - the VM is created and a (virtual) disk is created for it, but the operation of attaching the disk to the VM fails. Since I don't expect to use the API to create VMs (only to activate them and run programs on them), there is no reason to pursue this.