我在Linux上运行Oracle 12c，我只能使用sysdba参数登录sysadm但是当我删除SYSDBA参数时它失败
sqlplus sysadm/MYPASSWORD
SQL*Plus: Release 12.2.0.1.0 Production on Wed May 9 12:17:47 2018
Copyright (c) 1982, 2016, Oracle. All rights reserved.
ERROR:
ORA-01017: invalid username/password; logon denied
sqlplus sysadm/MYPASSWORD as sysdba
SQL*Plus: Release 12.2.0.1.0 Production on Wed May 9 12:17:30 2018
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
有什么建议吗？