On Ubuntu 12.04, when I `sudo -s` the $HOME variable is not changed, so if my regular user is `regularuser`, the situation goes like this:

```
$ cd
$ pwd
/home/regularuser
$ sudo -s
# cd
# pwd
/home/regularuser

```

I have abandoned Ubuntu a long time ago, so I cannot be sure, but I think this is the default behavior. So, my questions are:

1. How is this done? Where is the config?
2. How do I disable it?

**Edit:**
Thanks for the answers, which clarified things a bit, but I guess I must add a couple of questions, to get the answer I am looking for.

3. In Debian `sudo -s`, changes the $HOME variable to `/root`. From what I get from the answers and `man sudo` the shell ran with `sudo -s` is the one given in `/etc/passwd`, right?
4. However, on both Ubuntu and Debian the shell given in `/etc/passwd` for root is `/bin/bash`. In either system also, I cannot find where the difference in `.profile` or `.bashrc` files is, as far as $HOME is concerned, so that the behavior of `sudo -s` differs. Any help on this?