+*** Troubleshooting:
+
+- on ubuntu 20, I receive a failure on mkmf-gnome2 lib loading indicating missing
+ mkmf-gnome; "sudo gem install gtk3" workarounds this problem
+
+- if that fails on missing GTK header file (gtk.h), you can try to
+ inject cflags with such a command:
+
+ # perl -pi -e 's/(CXXFLAGS.*)/$1 `pkg-config --cflags gtk+-2.0`/' Makefile
+ # make
+
+- if that fails on redefinition of struct re_registers and you have
+ ruby-2.3, you can try to workaround with:
+
+ # cp /usr/include/ruby-2.3.0/ruby.h .
+ # perl -pi -e 's/.*HAVE_RUBY_ENCODING_H.*//' ruby.h
+ # make
+
+- if that fails on redefinition of struct re_registers and you have
+ ruby-2.5, you can try to workaround with:
+
+ # mkdir exiv2
+ # cp -a /usr/include/exiv2/* exiv2
+ # perl -pi -e 's/#define EXV_HAVE_REGEX 1//' exiv2/exv_conf.h
+ # make
+