Merge pull request #6538 from leeplay/patch-2

Update dockerlinks.md

docs/sources/userguide/dockerlinks.md

@@ -173,7 +173,7 @@ child container in two ways:
 
 Let's look first at the environment variables Docker sets. Let's run the `env`
 command to list the container's environment variables.
-    $docker run --rm --link --name web2 db:db training/webapp env
+    $ sudo docker run --rm --name web2 --link db:db training/webapp env
     . . .
     DB_NAME=/web2/db
     DB_PORT=tcp://172.17.0.5:5432