postmaster does not shut down

 when i grep for postmaster

ps -aef | grep postmaster

 

it says:

/usr/bin/postmaster -D /export/home1/sdc_image_pool/dbx -p 5432

 

when i try to stop postmaster doing

 

/usr/bin/pg_ctl -D /export/home1/sdc_image_pool/dbx/ stop

the following is displayed:

waiting for postmaster to shut down............................................................... failed
pg_ctl: postmaster does not shut down

i grepped for PGDATA

 

echo $PGDATA

it says undefined variable

 

please tell me what to do

 

thanks

regards

surabhi ahuja