How do I edit the mongodb.conf file? 

I want to change the bind\_ip from `127.0.0.1` to `0.0.0.0`. 

I have tried `sudo mongod --bind_ip 0.0.0.0`
I have tried manually editing the file (in a text editor), but it won't let me save.
I have tried changing the permissions of the file, yet I still can not save. 

I didn't create a mongodb.conf file either, so I'm not sure why it was automatically set up as 127.0.0.1

I'm using Ubuntu.

I've tried searching around but I haven't had any luck. 

All suggestions will be much appreciated.