ORA-01017 is a very common error which we get while connection to Oracle Database.
Other than invalid Username/Password, it can be encountered dute to improper connect string, permissions isues or wrong configuration of tnsnames.ora or sqlnet.ora.
Solution :
1) If connecting to Oracle 11 or later, passwords can be configured as case sensitive. To check this configuration, run following by SYS/SYSTEM user
SQL> show parameter SEC_CASE_SENSITIVE_LOGON
NAME TYPE VALUE
------------------------------ --------- ------------
sec_case_sensitive_logon boolean TRUE
You can change this configuration and alter password of user and try to connect
SQL> ALTER SYSTEM SET SEC_CASE_SENSITIVE_LOGON = FALSE;
System altered.
SQL> alter user scott identified by <password>;
User Altered.
SQL> CONN scott/<password>
Connected.
2) Check $ORACLE_SID and $ORACLE_HOME environmental variables to validate.
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3) Check whether the user we are trying to connect exists on that instance. Run following by SYS/SYSTEM user.
SQL> SELECT username FROM dba_users where username='SCOTT';
USERNAME
------------------------------
SCOTT
4) Check TNSNAMES.ORA to validate that TNS-Alias we are using to connect Oracle Database is pointing to right Database Server and Instance.