Updatedb is an alias for org.apache.nutch.crawl.CrawlDb
This class takes the output of the fetcher fetcher and updates the crawldb accordingly.
Usage:
bin/nutch updatedb <crawldb> (-dir <segments> | <seg1> <seg2> ...) [-force] [-normalize] [-filter] [-noAdditions]
<crawldb>: This is the path to the crawldb directory we wish to update.
-dir <segments>: This should be the path to the parent directory containing all, if several, segments to update from.
<seg1> <seg2> ...: Here we would pass a comprehensive list of paths to individual segmens to update from.
[-force]: This arguement will force an update even if the crawldb appears to be locked. 
: CAUTION: advised
[-normalize]: This arguement uses any current URLNormalizer's on urls in crawldb and segment (usually not needed).
[-filter]: Pass this arguement to use any current URLFilters on urls in the crawldb and segment. This can provide better quality results in certain applications.
[-noAdditions]: If pass this parameter the updatedb command will only update already existing URLs, and will not add any newly discovered URLs during a fetch.