The local instance of Oracle 12c runs under Solaris 11.3 and I can connect to it in sqlplus:
oracle@s11301:~$ sqlplus "/ as sysdba"
SQL*Plus: Release 12.2.0.1.0 Production on Wed May 30 21:42:13 2018
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
SQL> SELECT sys_context('USERENV', 'SID'), sys_context('userenv','instance_name') from dual;
SYS_CONTEXT('USERENV','SID')
--------------------------------------------------------------------------------
SYS_CONTEXT('USERENV','INSTANCE_NAME')
--------------------------------------------------------------------------------
13
orcl1
SQL>
But when I am testing a new connection to the same instance in SQL Developer, I get the following error:
The port number 1539 is from the listener.ora (I don't know why it is not 1521, but don't want to touch this yet) and the SID=orcl1 is what this instance was installed under.
Why SQL developer could not connect?