Only set SLURM_NPROCS if explicitly set by user on batch execute line.

src/srun/allocate.c

@@ -501,8 +501,10 @@ job_desc_msg_create_from_opts (char *script)
 
 		if (opt.overcommit)
 			putenv("SLURM_OVERCOMMIT=1");
-		xstrfmtcat(buf, "SLURM_NPROCS=%d", opt.nprocs);
-		putenv(buf);
+		if (opt.nprocs_set) {
+			xstrfmtcat(buf, "SLURM_NPROCS=%d", opt.nprocs);
+			putenv(buf);
+		}
 
 		j->environment = environ;
 		j->env_size = envcount (environ);