to debug why a plugin won't load even though it is found, you can run: $ ldd /path/to/plugin.so (this will print out all the libraries the given binary needs to load; if a library is not available on your system, it will be marked as "not found")
thanks for info. you are right. this is my result. it means the links broken? how to re-link or fix it? thanks, jonghyun
$ ldd ~/pd-externals/Gem/gem_imageMAGICK.so linux-vdso.so.1 => (0x00007ffe5294f000) libMagick++.so.4 => not found libMagickCore.so.4 => not found libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f03d08ef000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f03d052a000) libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f03d0314000) libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f03d000d000) /lib64/ld-linux-x86-64.so.2 (0x00005649f80b2000)