run_df_sim.py: command not found

[Mayflyworld]

Hello, there are some problems， i can't understand

dragon@dragon:/usr/src/rdf-sim$ su
Password:
root@dragon:/usr/src/rdf-sim# ./run_df_sim.py
bash: ./run_df_sim.py: Permission denied
root@dragon:/usr/src/rdf-sim#