I am trying to understand the following linker message. I have started GHCi, loaded a program and try to run it: Main> main ... Loading package poll-0.0 ... linking ... done. Loading package alsa-seq-0.6.0.3 ... can't load .so/.DLL for: /var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so (/var/cabal/lib/x86_64-linux-ghc-7.8.0.20140228/alsa-seq-0.6.0.3/libHSalsa-seq-0.6.0.3-ghc7.8.0.20140228.so: undefined symbol: alsazmseqzm0zi6zi0zi3_SystemziPosixziPoll_zdfStorableFd_closure) I assume that GHCi wants to say the following: The instance Storable Fd defined in module System.Posix.Poll cannot be found in the shared object file of the alsa-seq package. That's certainly true because that module is in the package 'poll' and not in 'alsa-seq'. But 'alsa-seq' imports 'poll'. What might be the problem? It's a rather big example that fails here, whereas the small examples in alsa-seq package work. Thus I first like to know what the message really means, before investigating further. I installed many packages at once with cabal-install using a single build directory, like: $ cabal install --builddir=/tmp/dist --with-ghc=ghc7.8.0.20140228 poll alsa-seq pkg1 pkg2 pkg3 ... ? Can this cause problems?