ORA-00257: Archiver error. Connect AS SYSDBA only until resolved.

ORA-00257: Archiver error. Connect AS SYSDBA only until resolved.
df -hP

Archive destination /oracle_db/db2 is 100% full

Need to delete some archive files + run RMAN backup

Once /oracle_db/db2 has space, issue 

ALTER SYSTEM SWITCH LOGFILE;

/dev/mapper/OraVG02-OraVol03   200G  25M  200G   100% /oracle_db/db2

To delete old archive files:

rman target /

DELETE OBSOLETE;

or

DELETE FORCE COPY OF ARCHIVELOG ALL;

once there is space, issue

ALTER SYSTEM SWITCH LOGFILE;

/dev/mapper/OraVG02-OraVol03   200G   33M  200G   1% /oracle_db/db2

Check Oracle Archive Mode
SELECT open_mode,database_role,log_mode FROM V$DATABASE;

OPEN_MODE            DATABASE_ROLE            LOG_MODE

-------------------- ------------------------ -----------

READ WRITE           PRIMARY                  ARCHIVELOG

Change Oracle Archive Mode

sqlplus / as sysdba

SQL> SHUTDOWN ABORT;

SQL> STARTUP RESTRICT;

SQL> SHUTDOWN IMMEDIATE;

SQL> STARTUP MOUNT;

SQL> ALTER DATABASE NOARCHIVELOG; / ALTER DATABASE ARCHIVELOG;

SQL> ALTER DATABASE OPEN;