Error while connecting Arduino to Macbook: “serial port already in use. try quitting any programs that may be using it”
Sorry about providing this as an answer, rather than comments; however, I do have some suggestions to troubleshoot the connection.

First, check the usb connections with lsusb

    lsusb |grep -i arduino


Similarly, you can try following the output of dmesg; though, I'm not sure about the version of dmesg your system's installation is running.  Newer version of dmesg have a "follow" option available. On my Fedora system it's:

    dmesg -wH


Check the output as you plug in the arduino for messages related to the device, such as the resulting location of the tty. As a desperate measure, you can also look in the /dev/ folder for the last modified device, and search your logs for those devices:

    ls -alrth /dev/