[chirp_users] CHIRP with Linux Mint / Linux Zorin

[Richard AG5M]

I am new to Linux (Linux Mint 17.2 and Zorin 9.0).  I have installed CHIRP on both computers.  But I am unable to download from my Baofeng UV-3R or Baofeng UV-5R.  In each case it appears it does not find, or allow me access to, the Com Port ttyS0, or any port for that matter.  Probably something simple I do not know about being new to Linux.  Can anyone please give me some advice?  Thanks
Richard AG5M