问题描述：使用 PL/SQL Developer 连接数据库时出现ORA-12541错误。

1.查询监听状态

[oracle@localhost admin]$ lsnrctl status

LSNRCTL for Linux: Version 19.0.0.0.0 - Production on 15-MAR-2025 10:47:57

Copyright (c) 1991, 2021, Oracle.  All rights reserved.

Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
TNS-12541: TNS:no listener
 TNS-12560: TNS:protocol adapter error
  TNS-00511: No listener
   Linux Error: 111: Connection refused

发现监听没启。

2.启动监听

[oracle@localhost admin]$ lsnrctl start