Question: Is it possible to disable direct login for normal users (like `oracle`) in Linux but allow `scp` and `sftp` for that use?

Answer: 
Methods such as creating the file `/etc/nologin`, setting account login shells to `/bin/false` or `/sbin/nologin` effectively disable user accounts from logging into an interactive shell, but do not protect the system.

If you want to specifically restrict a user to using `scp` or `sftp` only, install a restricted shell that is designed to do exactly that. The `rssh` package is a restricted shell designed to work with OpenSSH. 

```
: rssh is a restricted shell for use with OpenSSH, allowing only scp
: and/or sftp. For example, if you have a server which you only want
: to allow users to copy files off of via scp, without providing shell
: access, you can use rssh to do that. It is a alternative to scponly.

```

You should seriously consider setting a `chroot` for the users logging in with the restricted `rssh` shell. 

Read and understand the security implications of restricting users in such a way. Start with the `man` pages for `rssh` and `rssh.conf`. You should also understand what a `chroot` [is and how it works](https://unix.stackexchange.com/questions/105/chroot-jail-what-is-it-and-how-do-i-use-it).
The login shell can be changed from `bash` to `/usr/sbin/nologin` or `/bin/false` do prevent a normal login. The login shell can be changed with `usermod`:

```
usermod user_name -s /usr/sbin/nologin

```