我在ubuntu服务器上运行pgAgent和postgres。现在，pgAgent有时会丢失与服务器的连接，并且出现以下错误：
Mon Oct 8 11:47:14 2018 : WARNING: Couldn't create the primary connection (attempt 9): could not connect to server: Connection refused
Is the server running on host "127.0.0.1" and accepting
TCP/IP connections on port 5432?
Mon Oct 8 11:47:19 2018 : WARNING: Couldn't create the primary connection (attempt 10): could not connect to server: Connection refused
Is the server running on host "127.0.0.1" and accepting
TCP/IP connections on port 5432?
Mon Oct 8 11:47:19 2018 : ERROR: Stopping pgAgent: Couldn't establish the primary connection with the database server.
什么可能导致此行为？我该怎么做才能解决此问题？