ORA-01017: invalid username/password; logon denied - another silly case

It took some time to resolve it, although the cause was actually simple and silly. It occurred only on 12.1 CDB. 

Suddenly I was unable to logon as a common user locally into the root container without specifying the password in the command line. It was a test system, on production it worked well though. The connection over the network was OK : 

> sqlplus c##ddi

SQL*Plus: Release 12.1.0.2.0 Production on Mon Dec 13 17:42:16 2021

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Enter password:  
ERROR:
ORA-01017: invalid username/password; logon denied


Enter user-name: c##ddi
Enter password:  
ERROR:
ORA-01017: invalid username/password; logon denied


Enter user-name: ^C
> sqlplus c##ddi@\"ip_address/cdbm02_dev\"

SQL*Plus: Release 12.1.0.2.0 Production on Mon Dec 13 17:41:28 2021

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Enter password:
Last Successful login time: Mon Dec 13 2021 17:22:17 +03:00

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Advanced Analytics
and Real Application Testing options

C##DDI@ip_address/cdbm02_dev@CDB$ROOT hostname 13.12.21 17:41:31 > Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Advanced Analytics
and Real Application Testing options
>

The solution was to add a slash (/) after an username (:-D) :

> sqlplus c##ddi/

SQL*Plus: Release 12.1.0.2.0 Production on Mon Dec 13 17:44:30 2021

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Enter password:  
Last Successful login time: Mon Dec 13 2021 17:41:30 +03:00

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Advanced Analytics
and Real Application Testing options

C##DDI@cdbm02_dev@CDB$ROOT hostname 13.12.21 17:44:37 > Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Advanced Analytics
and Real Application Testing options

But the real cause of this was operating system PATH, which led to the place of  installed Oracle Instant Client, version 18.3. Starting sqlplus from ORACLE_HOME resolved the issue :

> $ORACLE_HOME/bin/sqlplus c##ddi      

SQL*Plus: Release 12.1.0.2.0 Production on Mon Dec 13 17:48:31 2021

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Enter password:  
Last Successful login time: Mon Dec 13 2021 17:44:37 +03:00

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Advanced Analytics
and Real Application Testing options

C##DDI@cdbm02_dev@CDB$ROOT hostname 13.12.21 17:48:37 >

Good Luck !