Unable to Start Scheduler

Question

I am new to Python and trying to install Airflow in my Mac, by following this tutorial

While these two commands work fine:

$ airflow initdb
$ airflow webserver -p 8080

The scheduler command (airflow scheduler) throws the following error:

 [2020-02-18 13:18:09,012] {scheduler_job.py:1382} ERROR - Exception when executing execute_helper Traceback (most recent call last):

  File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/jobs/scheduler_job.py", line 1380, in _execute
    self._execute_helper()

  File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/jobs/scheduler_job.py", line 1413, in _execute_helper
    self.processor_agent.start()

  File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/utils/dag_processing.py", line 554, in start
    self._process.start()

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/process.py", line 121, in start
    self._popen = self._Popen(self)

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/context.py", line 224, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/context.py", line 283, in _Popen
    return Popen(process_obj)

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 32, in __init__
    super().__init__(process_obj)

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 47, in _launch
    reduction.dump(process_obj, fp)

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)

AttributeError: Can't pickle local object 'SchedulerJob._execute.<locals>.processor_factory'

[2020-02-18 13:18:09,035] {helpers.py:322} INFO - Sending Signals.SIGTERM to GPID None

Traceback (most recent call last):    File "/Users/mac/Workspace/airflow/airflow_venv/bin/airflow", line 37, in <module>
    args.func(args)    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/utils/cli.py", line 75, in wrapper
    return f(*args, **kwargs)    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/bin/cli.py", line 1040, in scheduler
    job.run()    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/jobs/base_job.py", line 221, in run
    self._execute()    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/jobs/scheduler_job.py", line 1384, in _execute
    self.processor_agent.end()    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/utils/dag_processing.py", line 707, in end
    reap_process_group(self._process.pid, log=self.log)    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/utils/helpers.py", line 324, in reap_process_group
    signal_procs(sig)    File "/Users/mac/Workspace/airflow/airflow_venv/lib/python3.8/site-packages/airflow/utils/helpers.py", line 293, in signal_procs
    os.killpg(pgid, sig)

TypeError: an integer is required (got type NoneType)

Answer 1

EDIT: Python 3.8 is supported now https://github.com/apache/airflow#requirements. So this answer might not be relevant now.

This due to the Python version you are using. Airflow doesn't support Python 3.8 yet https://github.com/apache/airflow#stable-version-1109.

Downgrade your Python to 3.7 and check.