Paul, a "slot" is explicitly defined in the error message you copy/pasted:
"If none of a hostfile, the --host command line parameter, or an RM is present, Open MPI defaults to the number of processor cores" The error message also lists 4 ways on how you can move forward, but you should first ask yourself if you really want to run 12 MPI tasks on your machine. Cheers, Gilles On Sun, Nov 8, 2020 at 11:14 AM Paul Cizmas via users <users@lists.open-mpi.org> wrote: > > Hello: > > I just installed OpenMPI 4.0.5 on a Linux machine running Pop!_OS (made by > System76). The workstation has the following architecture: > > Architecture: x86_64 > CPU op-mode(s): 32-bit, 64-bit > Byte Order: Little Endian > Address sizes: 39 bits physical, 48 bits virtual > CPU(s): 16 > On-line CPU(s) list: 0-15 > Thread(s) per core: 2 > Core(s) per socket: 8 > Socket(s): 1 > NUMA node(s): 1 > Vendor ID: GenuineIntel > CPU family: 6 > > I am trying to run on the Linux box a code that I usually run on a Mac OS > without any issues. > > The script that I use is: > > exe='/usr/bin/mycode' # on jp2 > mympirun='/opt/openmpi/4.0.5/bin/mpirun' # GFortran on jp2 > $mympirun -np 12 $exe input1 > > I get the following error: > ==================================================== > No protocol specified > -------------------------------------------------------------------------- > There are not enough slots available in the system to satisfy the 12 > slots that were requested by the application: > > /usr/bin/mycode > > Either request fewer slots for your application, or make more slots > available for use. > > A "slot" is the Open MPI term for an allocatable unit where we can > launch a process. The number of slots available are defined by the > environment in which Open MPI processes are run: > > 1. Hostfile, via "slots=N" clauses (N defaults to number of > processor cores if not provided) > 2. The --host command line parameter, via a ":N" suffix on the > hostname (N defaults to 1 if not provided) > 3. Resource manager (e.g., SLURM, PBS/Torque, LSF, etc.) > 4. If none of a hostfile, the --host command line parameter, or an > RM is present, Open MPI defaults to the number of processor cores > > In all the above cases, if you want Open MPI to default to the number > of hardware threads instead of the number of processor cores, use the > --use-hwthread-cpus option. > > Alternatively, you can use the --oversubscribe option to ignore the > number of available slots when deciding the number of processes to > launch. > ======================================================= > > I do not understand “slots”. The architecture description of my Linux box > lists sockets, cores and threads, but not slots. > > What shall I specify instead of "-np 12”? > > Thank you, > Paul
