pg_dump and pg_dump all tools backup create zero size backup file from linux putty terminal

I have install postgres database version 9.6 , 10  on OS Centos 7 64 bit. trying to taken backup with this command

-bash-4.2$ pg_dump -h localhost -Fc backupdb > /var/lib/pgsql/niger_pgbackup/nigerpg_bkp.sql.

but problem is the backup file size had zero . I have tried many time. Kindly help where i have wrong.

-bash-4.2$ pg_dump -h localhost -Fc backupdb > /var/lib/pgsql/niger_pgbackup/nig erpg_bkp.sql
-bash-4.2$ cd niger_pgbackup/
-bash-4.2$ ls -ltr
total 0
-rwxrwxrwx 1 postgres postgres 0 Oct 7 23:38 nigerpg_bkp.sql

Regards

Niger