Encountered ​​SQL developer- the network adapter could not establish the connection​​, it is quite simple, the Oracle listener was not start up. Resolved by below command, after startup the listener, can connect through SQL developer with successful result.

Error 1: Oracle SQL Developer error - IO Error: The Network Adapter could not establish the connection.
Error 2: cannot connect through OEM, Oracle Enterprise Manager.

Below are two solutions,

Start listener

[tom@ocp admin]$ lsnrctl start

LSNRCTL for Linux: Version 11.2.0.1.0 - Production on 21-12月-2018 20:18:20

Copyright (c) 1991, 2009, Oracle.  All rights reserved.

启动/u01/app/tom/product/11.2.0/dbhome_1/bin/tnslsnr: 请稍候...

TNSLSNR for Linux: Version 11.2.0.1.0 - Production
系统参数文件为/u01/app/tom/product/11.2.0/dbhome_1/network/admin/listener.ora
写入/u01/app/tom/diag/tnslsnr/ocp/listener/alert/log.xml的日志信息
监听: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=ocp)(PORT=1521)))

正在连接到 (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=ocp)(PORT=1521)))
LISTENER 的 STATUS
------------------------
别名                      LISTENER
版本                      TNSLSNR for Linux: Version 11.2.0.1.0 - Production
启动日期                  21-12月-2018 20:18:20
正常运行时间              0 天 0 小时 0 分 0 秒
跟踪级别                  off
安全性                    ON: Local OS Authentication
SNMP                      OFF
监听程序参数文件          /u01/app/tom/product/11.2.0/dbhome_1/network/admin/listener.ora
监听程序日志文件          /u01/app/tom/diag/tnslsnr/ocp/listener/alert/log.xml
监听端点概要...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=ocp)(PORT=1521)))
监听程序不支持服务
命令执行成功
[tom@ocp admin]$

Start OEM, Oracle Enterprise Manager

[tom@ocp bin]$ emctl start dbconsole
Oracle Enterprise Manager 11g Database Control Release 11.2.0.1.0
Copyright (c) 1996, 2009 Oracle Corporation.  All rights reserved.
https://ocp:1158/em/console/aboutApplication
Starting Oracle Enterprise Manager 11g Database Control ..... started.
------------------------------------------------------------------
Logs are generated in directory /u01/app/tom/product/11.2.0/dbhome_1/ocp_orcl/sysman/log
[tom@ocp bin]$ pwd
/u01/app/tom/product/11.2.0/dbhome_1/bin
[tom@ocp bin]$

Use below link to access OEM, Oracle Enterprise Manager
​​​https://192.168.26.130:1158/em/​​ username / password = sys/oracle, role as sysdba

Below command to check the EM port usage,

[tom@ocp ~]$ cd $ORACLE_HOME
[1]+  Exit 255                LANG=zh_CN.utf8 dbca  (wd: ~)
(wd now: /u01/app/tom/product/11.2.0/dbhome_1)
[tom@ocp dbhome_1]$ cd install/
[tom@ocp install]$ ls
chainedInstall  envVars.properties  make.log  portlist.ini  root_ocp_2018-12-19_21-20-28.log  utl
config          jlib                oratab    readme.txt    unix
[tom@ocp install]$ cat portlist.ini
Enterprise Manager Console HTTP 端口 (orcl) = 1158
Enterprise Manager 代理端口 (orcl) = 3938
[tom@ocp install]$ pwd
/u01/app/tom/product/11.2.0/dbhome_1/install
[tom@ocp install]$

Reference

​​SQL developer- the network adapter could not establish the connection​​