sudo https_proxy="https://username:password@your_proxy:proxy_port" dropbox start -i
[sudo] password for ozberk: 
Starting Dropbox...nonnumeric port: 'proxy_port'
Traceback (most recent call last):
  File "/usr/bin/dropbox", line 388, in error
    self.download.url, ex))
  File "/usr/bin/dropbox", line 240, in get_download_debug_info
    msg = "\nURL that failed to download: %s\nError: %s\n" % (url, e.strerror)
AttributeError: 'InvalidURL' object has no attribute 'strerror'