Postgresql starts but nothing 's happened

Hi

I'm a french user. I have installed a 7.1 postgresql version on my linux server. (Redhat 7.2)

I have a problem with starting postgresql.

I initialize database with initdb then I modify data in postgresql.conf file.
After that I run the postmaster with the -i option and when I want to test something like createdb, it starts to do something and stays in this state. I don't have the postgresql prompt !
Nothing's happen, the server works but like if it'd be crashed.
When I type e.g. psql template1 it makes nothing too.

I am a newbie in linux and postgresql and I am lost in all these configurations I have to do !!!
Please help me

Thanks by advance.
Pierre-Alexis