Im trying to take all backup by running these as superuser i.e postgres but
pg_dumpall > alldb.sql
bash: alldb.sql: Permission denied
pg_dumpall works but give backup as text in terminal
made changes in pg_hba.conf
This has nothing to do with pg_dumpall or pg_hba. It is just the shell complaining that it cannot write to the current directory. Try another directory to put your file into, for example:
pg_dumpall > /tmp/alldb.sql