oracle 12c rac switch from mounted to open

Question

How to open an RAC database correctly(version 12.1) from "mounted" state?

Earlier, nodes #01 and #02 were opened manually by the command alter database open.

Now, the database in this state:

SQL> select instance_name,status from gv$instance;
INSTANCE_NAME    STATUS
node01          OPEN
node02          OPEN
node04          MOUNTED
node03          MOUNTED

~$ srvctl status database -d cldb -v
Instance node01 is running on node srv-n01. Instance status: Open,Readonly.
Instance node02 is running on node srv-n02. Instance status: Open,Readonly.
Instance node03 is running on node srv-n03. Instance status: Mounted (Closed).
Instance node04 is running on node srv-n04. Instance status: Mounted (Closed).

Answer 1

Connect to third instance and issue

SQL> alter database open;

then to fourth instance and do the same.

But if you want to open all instances at once, you need to use srvctl utility:

srvctl start database -db db_name

https://docs.oracle.com/database/121/RACAD/GUID-C9DB4DCB-34B9-42F0-8AB4-33199087CE98.htm#RACAD900