returning true when no SD Card present.

First time poster here, so sorry if I do this wrong.

I'm currently trying to get my code to tell me whether or not a file was successfully found or not for troubleshooting proposes. Here's the code in question:
File dataFile ="/mnt/sda1/V2_2_Data.txt", FILE_APPEND);
Serial.println("Not Found");
Even when my sd card is not plugged in it still registers the file was opened succesfully. (I always get a bol value of 1 for dataFile when I don't think I should.

I thought since the SD card wasn't plugged in dataFile should return 0 and not 1. I shelled into the yun I am using and I cannot go to the directory since there is no SD Card plugged in, is that my issue?

So I found the issue, but not a solution. Turns out the arduino Yun doesn't unmount the SD card when unplugged. Does anyone know a way to unmount from either the unix or the arduino side of the board?