# FAQs

1. Why am I seeing weird “symbol not found” errors while trying to import mdtraj?

   Let me guess – you’re using a Linux cluster running CentOS 5? Your system compiler is gcc 4.1?

   You need a more recent version of gcc (>= 4.4). You can set the `CC` and `CXX` environment variables to point to a different compiler.

   Unfortunately, installing from conda will not help you here. You must compile from source on CentOS 5 (or similar).

   For Pande lab members on `vsp-compute`, set the following environment variables and compile from source

       $ export CC=gcc44
       $ export CXX=g++44
       $ python setup.py install