$ mongorestore -d config -c changelog config/changelog.bson
connected to: 127.0.0.1
2015-03-19T08:31:07.496+1100 config 2/config/changelog.bson
2015-03-19T08:31:07.496+1100 	going into namespace [config.changelog]
2015-03-19T08:31:07.500+1100 	Created collection config.changelog with options: { "create" : "changelog", "size" : 10485760, "capped" : true }
25528 objects found
2015-03-19T08:31:08.492+1100 	Creating index: { key: { _id: 1 }, ns: "config.changelog", name: "_id_" }

$ mongorestore -d config -c changelog config/changelog.bson
2015-03-19T08:32:07.279+1100	checking for collection data in config 2/config/changelog.bson
2015-03-19T08:32:07.280+1100	reading metadata file from config 2/config/changelog.metadata.json
2015-03-19T08:32:07.281+1100	Failed: restore error: config.changelog: error creating collection config.changelog: error running create command: exception: specify size:<n> when capped is true