Postmaster environment variables

I am trying to relocate my database,  as per instructions in the manual:

Under user postgres :

sh-2.04$ PGDATA2=/home/postgres/data
sh-2.04$ export PGDATA2
sh-2.04$ echo $PGDATA2
/home/postgres/data

I stop the postmaster and :
sh-2.04$ /usr/lib/postgresql/bin/initlocation PGDATA2
The location will be initialized with username "postgres".
This user will own all the files and must also own the server process.

Fixing permissions on pre-existing directory /home/postgres/data
Fixing permissions on pre-existing directory /home/postgres/data/base

initlocation is complete. (...)

I restart the postmaster and :

sh-2.04$ createdb planifgr -D 'PGDATA2'
ERROR:  Postmaster environment variable 'PGDATA2' not set
createdb: database creation failed

although :

sh-2.04$ echo $PGDATA2
/home/postgres/data

I even tried to set the variable from within the scripts (debian distr.)
that start the backend (etc/init.d/postgresql). Same response.

Where is the variable?