WAL level not sufficient for making an online backup

I have tried to do database replication in linux 7.0 red hat using postgresql.

I refered this URL for Confuring http://blog.terminal.com/postgresql-replication-and-backup-methods/ I completed the the steps upto this step

5. Configuring the slave server

but the step

6. Initial replication

when I executed this command in Master

-bash-4.2$ psql -c "select pg_start_backup('initial_backup');"

I got Error Like this

ERROR:  WAL level not sufficient for making an online backup
HINT:  wal_level must be set to "archive" or "hot_standby" at server start.

So kindly let me know where we are wrong.