I use GIMP which runs on Linux and has several sharpening filters, among others. But, as others here have already said, if the original image doesn't have the necessary information (e.g., blurry, unfocused, etc) no amount of technical work is going to give you something which isn't there to begin with.
I use GIMP which runs on Linux and has several sharpening filters, among others. But, as others here have already said, if the original image doesn't have the necessary information (e.g., blurry, unfocused, etc) no amount of technical work is going to give you something which isn't there to begin with.