title: UHD error with REDHAWK
body: <p>I made a node which contains a USRP_UHD and a GPP (and make sure the ip_address is correct for USRP_UHD). I launched the domain based on this node. However, I got the following error:</p>
  
  <pre><code>UHD Error:
      Device discovery error: AssertionError: libusb_init(&amp;_context) == 0
        in libusb_session_impl::libusb_session_impl()
        at /builddir/build/BUILD/uhd-release_003_005_003/host/lib/transport/libusb1_base.cpp:37
  
  UHD Error:
      Device discovery error: AssertionError: libusb_init(&amp;_context) == 0
        in libusb_session_impl::libusb_session_impl()
        at /builddir/build/BUILD/uhd-release_003_005_003/host/lib/transport/libusb1_base.cpp:37
  ...
  -- Opening a USRP2/N-Series device...
  -- Current recv frame size: 1472 bytes
  -- Current send frame size: 1472 bytes
  
  UHD Warning:
      Unable to set the thread priority. Performance may be negatively affected.
      Please see the general application notes in the manual for instructions.
      EnvironmentError: OSError: error in pthread_setschedparam
  </code></pre>
  
  <p>I did get two unallocated (TX/RX for each) tuners, but it is not easy to allocate these two tuners for use for any parameters.</p>
  
  <p>Besides, if I just launch the domain and launch the single device USRP_UHD, or simply run the discover USRP_UHD command via the command line window, I got the same error:</p>
  
  <pre><code>UHD Error:
      Device discovery error: AssertionError: libusb_init(&amp;_context) == 0
        in libusb_session_impl::libusb_session_impl()
        at /builddir/build/BUILD/uhd-release_003_005_003/host/lib/transport/libusb1_base.cpp:37
  2016-02-01 16:59:20 WARN  USRP_UHD_i:943 - WARNING: NO UHD (USRP) DEVICES FOUND!
  </code></pre>
  
  <p>Could anybody figure out where this problem is? Thanks in advance! </p>