嗨，
我在笔记本电脑上安装了Oracle 11g 用于练习 Oracle。
我已连接到 HR 帐户。它已经连接了 3 天，但之后我尝试通过 SQL Developer 连接时出现此错误：
TNS-12505: TNS:listener does not currently know of SID given in connect descriptor
【问题讨论】：
标签： oracle oracle11g database-connection
确保
您的数据库已启动；
$ sqlplus / as sysdba
SQL> startup
ORACLE_SID 参数设置为路径值；
在 Windows 上，通过以下方式查找：
C:\Users\pc> echo %ORACLE_SID%
mydb
在 Unix 上，查找方式：
$ echo $ORACLE_SID
mydb
并且 Listener 正在运行：
$ lsnrctl status
LSNRCTL for Linux : Version 12.1.0.2.0 - Production on 03-JUN-2018 09:31:07
Copyright (c) 1991, 2014, Oracle. All rights reserved.
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 12.1.0.2.0 - Production
Start Date 30-MAR-2018 22:29:45
Uptime 53 days 11 hr. 1 min. 10 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /u01/app/12.1.0.2/grid/network/admin/listener.ora
Listener Log File /u01/app/grid/diag/tnslsnr/mydb/listener/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=172.16.15.81)(PORT=1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=mycompany.com)(PORT=5505))(Presentation=HTTP)(Session=RAW))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcps)(HOST=mycompany.com)(PORT=5506))
(Security=(my_wallet_directory=/u01/app/oracle/product/12.1.0.2/dbhome_1/admin/mydb/xdb_wallet))(Presentation=HTTP)(Session=RAW))
Services Summary...
Instance "mydb", status READY, has 1 handler(s) for this service...
The command completed successfully
【讨论】：
[oracle@oracl oracle]$ lsnrctl status ... Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=oracl)(PORT=1521))) ... Listener Parameter File path_to/listener.ora Listener Log File path_to/log.xml Listening Endpoints Summary... (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=oracl)(PORT=1521))) (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521))) The listener supports no services The command completed successfully
SQL> alter system register;注册监听器
SID_LIST_LISTENER = (SID_LIST = (SID_DESC= (GLOBAL_DBNAME=oracl) (ORACLE_HOME=/u01/app/oracle/product/19c/dbhome_1) (SID_NAME=orcl) ) ) ADR_BASE_LISTENER=/u01/app/oracle
lsnrctl status 命令显示状态为未知：Services Summary... Service "oracl" has 1 instance(s). Instance "orcl", status UNKNOWN, has 1 handler(s) for this service...。不好吗？