I've had a lot of trouble reinstalling ipkg for a NAS 214+. My old source of info has gone, but a web search turned up this blog that covers with good working instructions installing a community source for ipkg and for a GUI version that works very well. No hassle identifying the right package for processor type. Once the source is added to Package Centre, the ipkg command line utility is called Easy Bootstrap Installer and the GUI interface iPKGui. Now I've got utilities like "man", "rename". And "fdupes", which was the original reason for my search. I see "fslint" is there too. I hope this saves someone else the bother of hunting down how to get some of those familiar Linux utilities onto their NAS. Just shoved this guy a small Paypal contribution. Here's the link:
How to Install IPKG on Synology NAS
Trustworthy expert guide to your Synology Nas.