There are several solutions for RGB to CMYK convertion in GIMP that suggest using Separate including this one: Converting RGB to CMYK color profile in GIMP. I've have followed the simple instructions to install it, but the option does not appear in the Image menu of GIMP. I have copied the separate executable into the .gimp plugs folder, which I know is correct because I have placed other executables there successfully. Also, I had earlier built LCMS from source. The only evidence I have that LCMS is installed correctly, though, is that ImageMagick no longer reports an error when I use the ICC option on convert. How can I get I get Separate working in GIMP 2.8 on Ubuntu 14.0.4?
The answer was in this link https://askubuntu.com/questions/44132/how-do-i-install-libtiff-so-3 I created the symbolic link as suggested and it worked. Also, running gimp from terminal with --verbose is helpful!