Changing SYS Password in Dataguard Environment

If you change SYS password with ALTER USER SYS IDENTIFIED BY NEWPASSWORD on the primary database of a dataguard environment, primary side stops to transfer archivelogs to standby and you will see an error on primary database alertlog file like:

------------------------------------------------------------------
Check that the primary and standby are using a password file
and remote_login_passwordfile is set to SHARED or EXCLUSIVE,
and that the SYS password is same in the password files.
returning error ORA-16191
------------------------------------------------------------------

This is because "If you issue the ALTER USER statement to change the password for SYS, both the password stored in the data dictionary and the password stored in the password file are updated." So your password file is updated in primary side but not in standby side.

In this situation set your password file in standby server with:
orapwd file=$ORACLE_HOME/dbs/orapwSID password=newpassword; (don't forget to move/delete old one)

Conclusion: If you're going to change your sys password in a dataguard environment you must set the password files with new password in both primary and standby servers.