title: mpirun: Unrecognized argument mca
body: <p>I have a c++ solver which I need to run in parallel using the following command:</p>
  
  <pre><code>nohup mpirun -np 16 ./my_exec &gt; log.txt &amp;
  </code></pre>
  
  <p>This command will run <code>my_exec</code> independently on the 16 processors available on my node. This used to work perfectly. </p>
  
  <p>Last week, the HPC department performed an OS upgrade and now, when launching the same command, I get two warning messages (for each processor). The first one is:</p>
  
  <pre><code>--------------------------------------------------------------------------                           
  2 WARNING: It appears that your OpenFabrics subsystem is configured to only                            
  3 allow registering part of your physical memory.  This can cause MPI jobs to                          
  4 run with erratic performance, hang, and/or crash.                                                    
  5                                                                                                      
  6 This may be caused by your OpenFabrics vendor limiting the amount of                                 
  7 physical memory that can be registered.  You should investigate the                                  
  8 relevant Linux kernel module parameters that control how much physical                               
  9 memory can be registered, and increase them to allow registering all                                 
  10 physical memory on your machine.                                                                     
  11                                                                                                      
  12 See this Open MPI FAQ item for more information on these Linux kernel module                         
  13 parameters:                                                                                          
  14                                                                                                      
  15     http://www.open-mpi.org/faq/?category=openfabrics#ib-locked-pages                                
  16                                                                                                      
  17   Local host:              tamnun                                                                    
  18   Registerable memory:     32768 MiB                                                                 
  19   Total memory:            98294 MiB                                                                 
  20                                                                                                      
  21 Your MPI job will continue, but may be behave poorly and/or hang.                                    
  22 --------------------------------------------------------------------------                           
  23 --------------------------------------------------------------------------        
  </code></pre>
  
  <p>I then get an output from my code, which tells me it thinks I am launching only 1 realization of the code (<code>Nprocs</code> = 1 instead of 16).</p>
  
  <pre><code>177                                                                                                      
  178 # MPI IS ON; Nprocs = 1                                                                              
  179 Filename = ../input/odtParam.inp                                                                     
  180                                                                                                      
  181 # MPI IS ON; Nprocs = 1                                                                              
  182                                                                                                      
  183 ***** Error, process 0 failed to create ../data/data_0/, or it was already there
  </code></pre>
  
  <p>Finally, the second warning message is:</p>
  
  <pre><code>185 --------------------------------------------------------------------------                           
  186 An MPI process has executed an operation involving a call to the                                     
  187 "fork()" system call to create a child process.  Open MPI is currently                               
  188 operating in a condition that could result in memory corruption or                                   
  189 other system errors; your MPI job may hang, crash, or produce silent                                 
  190 data corruption.  The use of fork() (or system() or other calls that                                 
  191 create child processes) is strongly discouraged.                                                     
  192                                                                                                      
  193 The process that invoked fork was:                                                                   
  194                                                                                                      
  195   Local host:          tamnun (PID 17446)                                                            
  196   MPI_COMM_WORLD rank: 0                                                                             
  197                                                                                                      
  198 If you are *absolutely sure* that your application will successfully                                 
  199 and correctly survive a call to fork(), you may disable this warning                                 
  200 by setting the mpi_warn_on_fork MCA parameter to 0.                                                  
  201 --------------------------------------------------------------------------     
  </code></pre>
  
  <p>After looking around online, I tried following the warning messages' advice by setting the <code>MCA</code> parameter <code>mpi_warn_on_fork</code> to 0 with the command:</p>
  
  <pre><code>nohup mpirun --mca mpi_warn_on_fork 0 -np 16 ./my_exec &gt; log.txt &amp;
  </code></pre>
  
  <p>which yielded the following error message:</p>
  
  <pre><code>[mpiexec@tamnun] match_arg (./utils/args/args.c:194): unrecognized argument mca
  [mpiexec@tamnun] HYDU_parse_array (./utils/args/args.c:214): argument matching returned error
  [mpiexec@tamnun] parse_args (./ui/mpich/utils.c:2964): error parsing input array
  [mpiexec@tamnun] HYD_uii_mpx_get_parameters (./ui/mpich/utils.c:3238): unable to parse user arguments
  </code></pre>
  
  <p>I am using RedHat 6.7 (Santiago). I contacted the HPC department, but since I am in a university, this issue may take them a day or two to respond. Any help or guidance would be appreciated.</p>
  
  <p><strong>EDIT in response to answer:</strong></p>
  
  <p>Indeed, I was compiling my code with Open MPI's <code>mpic++</code> while running the executable with Intel's <code>mpirun</code> command, hence the error (after the OS upgrade Intel's <code>mpirun</code> was set as the default). I had to put the Open MPI's <code>mpirun</code>'s path at the beginning of the <code>$PATH</code> environmental variable. </p>
  
  <p>The code now runs as expected BUT I still get the first warning message above (it does not advise me to use the <code>MCA</code> parameter <code>mpi_warn_on_fork</code> anymore. I think (but not sure) it is an issue I need to resolve with the HPC department. </p>