I have recently upgraded from 16.04 to 18.04 While trying to start qjack I get this error
qjackctl: relocation error: /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5: symbol png_set_option version PNG16_0 not defined in file libpng16.so.16 with link time reference
So I tried reinstalling qjack, all the qt5 lib and the libpng16 lib to no avail. So I had a deeper look at the libpng in question and checked the symbols.
readelf -Ws /usr/lib/x86_64-linux-gnu/libpng16.so.16 | grep png_set_option
84: 0000000000008e00 89 FUNC GLOBAL DEFAULT 13 png_set_option@@PNG16_0
So the png_set_option is actually defined for PNG16_0 isn't it? I don't really know what to do to correct this.
So I located the different versions of libpng16
I tried to find the lib which did not have the right symbol
This does not return anything (symbol is absent)
So I made a symbolic link from the bad lib /usr/local/lib/libpng16.so.16 to the good one /usr/lib/x86_64-linux-gnu/libpng16.so.16
Hope this help, unfortunately this can be broken when updating. Don't forget to backup /usr/local/lib/ before in case you break it
This solution is inspired from this post