# 4.5. Filesystem requirements

Warning

If you are building Open MPI on a network filesystem, the machine you on which you are building must be time-synchronized with the file server.

Specifically: Open MPI’s build system requires accurate filesystem timestamps. If your `make` output shows that it ran GNU Automake, Autoconf, and/or Libtool, or includes warning about timestamps in the future, perhaps looking something like this:

    Warning: File `Makefile.am' has modification time 3.6e+04 s in the future

Know that this is not normal, and you likely have an invalid build.

In this case, you should remove the Open MPI source directory and start over (e.g., by re-extracting the Open MPI tarball): either switch to build on a local filesystem, or ensure that the time on your build machine is synchronized with the time on your file server before building again.