Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources?

I packaged a Jar and used spark-submit to run the app in spark

but I got the following error. Initial job has not accepted any resources; check your cluster UI to ensure that workers are registered and have sufficient resources my cpu info

$ free -m
              total        used        free      shared  buff/cache   available
Mem:          15886       12206        1984          16        1695        3251
Swap:          2047         216        1831

this is my spark_env.sh:

export SPARK_EXECUTOR_INSTANCES=4
export SPARK_EXECUTOR_CORES=4
export SPARK_EXECUTOR_MEMORY=2G

export SPARK_UI_PORT=4040

export SPARK_MASTER_PORT=7077
export SPARK_MASTER_WEBUI_PORT=8099

export SPARK_WORKER_CORES=4
export SPARK_WORKER_INSTANCES=4
export SPARK_WORKER_MEMORY=2G

Is there any problem with my spark_env.sh?