pg_dump

I've install postgres in linux.
but pg_dump its not working at all.
if i execute the pg_dump to the file like this

pg_dump -Upostgres -dpostgres > file.dmp

the file file.dmp is empty

and if i execute the psql with list database option, the result is error

-bash-3.00$ psql -l
ERROR: relation "pg_catalog.pg_user" does not exist

can any one help me

Thanx

tosa

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