ORA-65066: The specified changes must apply to all containers

Symptom:

   We try to modify sys system password in a PDB(pluggable DB). It error out with code

   ORA-65066: The specified changes must apply to all containers
    The reason is sys system are common users among CDB and PDB  link oracle doc link

    So PDBs do not have their own sys system users,  they are inherited from CDB$ROOT

Solution:

  sqlplus / as sysdba to login  CDB$ROOT
SQL> show con_name

CON_NAME
------------------------------
CDB$ROOT
SQL>alter user system identified by XXXXXX;