报错现象
今天给客户一个单实例环境配置监听，创建正常，查询状态异常报错
tns 12541 tns 12560 tns 00511 linux error 111:connection refused
匹配MOS
Starting TNS Listener or LSNRCTL Start Yields TNS-12541, Linux Error: 111: Connection Refused (文档 ID 343295.1)
>lsnrctl status
Any of the following listener error stacks might be thrown:
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=<hostname>)(PORT=1521)))
TNS-12541: TNS:no listener
TNS-12560: TNS:protocol adapter error
TNS-00511: No listener
Linux Error: 111: Connection refused
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC)))
TNS-12537: TNS:connection closed
TNS-12560: TNS:protocol adapter error
TNS-00507: Connection closed
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=<hostname>)(PORT=1521)))
TNS-12547: TNS:lost contact
TNS-12560: TNS:protocol adapter error
TNS-00517: Lost contact
Linux Error: 104: Connection reset by peer
CHANGES
This is likely a new installation.
CAUSE
1. There is possibly an incorrect IP Address specified for the host in the /etc/hosts file.
For example:
192.xxx.yyy.zzz <hostname>.<domain name>
Whereas the actual ip address for the host "<hostname>.<domain name>" is 192.aaa.bbb.ccc
2. Also, the localhost reference may be incorrect or missing from the /etc/hosts file.
3. Oracle may not have read access to /etc/nsswitch.conf file.
SOLUTION
To implement the solution, please execute the following steps:
1. Correct the mapping in the /etc/hosts file by adding/correcting the IP address and/or hostname reference for the Unix/Linux Server (both long and short host names).
For example:
# Add or edit the /etc/hosts file to include a valid entry for the Server:
192.aaa.bbb.ccc <hostname>.<domain name> <hostname>
2. Check that the localhost loopback name and address are correct (both long and short host names).
An example of a correct localhost entry would be as follows:
127.0.0.1 localhost.localdomain localhost
3. Remember to save the /etc/hosts file and then start the listener.
本次是配置/etc/hosts文件时，未注意直接清空/etc/hosts文件导致Localhost信息丢失，最终导致监听程序无法正常运行
4. Check permissions on /etc/nsswitch.conf file to ensure group and other have read access.
- If necessary change permisions on /etc/nsswitch.conf as follows:
chmod 644 /etc/nsswitch.conf
