Cant you do a search for *.tga in the gamedata directory and drag them into xnview / xnconvert? At least xnconvert batch converts them flawlessly here when I tell it to use exactly the filename of the original (default setting adds _result to the filename), save to original folder and delete the originals, I use Windows x64 though and my last experience with linux is from several years ago sorry. It is really like drag search results over to xnconvert, drop, three clicks and a few seconds of waiting. Ok it´s a SSD, but still, no big deal.