What if I don't know the original shell?

If you don't know the original shell of a user, you can check it by looking at the /etc/passwd file. Here’s how to do it:

Use the grep command to find the user entry:
```
grep 'joker' /etc/passwd
```
The output will look something like this:
```
joker:x:5001:5001::/home/joker:/bin/bash
```
The last field (after the last colon) indicates the user's current shell. In this example, it shows /bin/bash.

Once you identify the original shell, you can revert to it using the usermod command as previously described. If you have any more questions, feel free to ask!