Using multidir

Dear all,
i am trying to run a calculation using this:
mpirun -np 4 gmx_mpi mdrun -deffnm md -multidir 0 1 2 3
but I faced this error:
Inconsistency in user input:
The number of ranks (1) is not a multiple of the number of simulations (4)

The machine I’m working with has a single GPU with 24 processors.
I don’t know what the problem is.

Something seems to be wrong with the mpirun invocation as mdrun says that it only has a single MPI rank. Are you using an mpirun that is compatible with the MPI library you used for compiling GROMACS? And is -np the correct option for specifying the number of ranks?