How to enable PITR on all POSTGRES server

Hello,
While Performing the Online Recovery By PITR, We had a Problem as we didnt Understand the proper Way of Enabling PITR on all POSTGRES Server .
again , when

psql -c "select pg_start_backup('pgpool-recovery')" postgres
is executed, the following msg appeared.
===================
WAL archive is not active
archive command must be defined before onlime backups can be made
=================
so , how can we proceed further , a help is needed !!!
with regards
Ntech

re: How to enable PITR on all POSTGRES server

in postgresql.conf

archive_mode = on # for pgpoolII
archive_command = 'date >&2 && echo did dummy archiving for %f >&2 ' # for pgpoolII