Arduino UNO R3 on Raspberry Pi 2 - Error Message

I get the following error message (verbose mode enabled) when I try to download a sketch to an R# from a Raspberry Pi 2.

Anyone with a hint?

avrdude: Version 6.1, compiled on Jul  7 2015 at 10:29:47
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2014 Joerg Wunsch

         System wide configuration file is "/usr/share/arduino/hardware/tools/avrdude.conf"
         User configuration file is "/home/pi/.avrduderc"
         User configuration file does not exist or is not a regular file, skipping

         Using Port                    : /dev/ttyACM1
         Using Programmer              : arduino
         Overriding Baud Rate          : 115200
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00

You sure it's being assigned ttyACM1?

If you disconnect and reconnect the Arduino, and then run "dmesg" right away, you'll see what it is enumerated as.

It's the same message I get in Ubuntu if I try to write to a port with nothing connected to it or the device powered off.