.. _faq-label:

Frequently Asked Questions
==========================

Why do I get message that say "... GLIBCXX_3.4.20 not found ..." when
I try to run any application when XALT is active?

    This means that your site has installed an GCC version newer than
    the default gcc installed on the system. Please re-install XALT
    with just the system version of gcc.  If your system gcc is older
    than 4.8.5 (say Centos 6) then please see :ref:`old_gcc-label`


Why when my site upgraded to Centos 7.5 and the latest OPA drivers for
Intel's Omni-Path and using Intel MPI, all XALT built programs have an
error that looks like this? 

    c591-801.stampede2.tacc.utexas.edu.334447hfi_userinit: mmap of status page (dabbad0008030000) failed: Operation not permitted
    c591-801.stampede2.tacc.utexas.edu.334447hfp_gen1_context_open: hfi_userinit: failed, trying again (1/3)


    This is because all programs built with XALT prior to version 2.5
    caused the GNU Stack bit to be set.  Please see
    :ref:`execstack_bit-label` for a migration strategy.