Restart Data Guard physical standby database

On primary:

# Defer the standby archive log destination

SQL> alter system set log_archive_dest_state_2=defer scope=both;

System altered.

SQL> alter system switch logfile;

System altered.

Shutdown and startup mount the standby database:

SQL> shutdown immediate;
ORA-01109: database not open


Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  835104768 bytes
Fixed Size                  2259800 bytes
Variable Size             285213864 bytes
Database Buffers          541065216 bytes
Redo Buffers                6565888 bytes
Database mounted.
SQL>

In case Data Guard Broker is configured, no other steps are required after restart of standby database.