【异常】lockfile.AlreadyLocked: ~/airflow/airflow-scheduler.

File "/usr/bin/airflow",line 32,in <module>
    args.func(args)
  File "/usr/lib/python2.7/site-packages/airflow/utils/cli.py",line 74,in wrapper
    return f(*args,**kwargs)
  File "/usr/lib/python2.7/site-packages/airflow/bin/cli.py",line 1000,in scheduler
    with ctx:
  File "/usr/lib/python2.7/site-packages/daemon/daemon.py",line 397,in __enter__
    self.open()
  File "/usr/lib/python2.7/site-packages/daemon/daemon.py",line 389,in open
    self.pidfile.__enter__()
  File "/usr/lib/python2.7/site-packages/lockfile/__init__.py",line 197,in __enter__
    self.acquire()
  File "/usr/lib/python2.7/site-packages/daemon/pidfile.py",line 60,in acquire
    super(TimeoutPIDLockFile,self).acquire(timeout,*args,**kwargs)
  File "/usr/lib/python2.7/site-packages/lockfile/pidlockfile.py",line 88,in acquire
    self.path)
lockfile.AlreadyLocked: /home/cloudera-scm/airflow/airflow-scheduler.pid is already locked