In my case mongodb packages are named mongodb-org and mongodb-org-*
So when I type sudo apt purge mongo then tab (for auto-completion) I can see all installed packages that start with mongo.
Another option is to run the following command (which will list all packages that contain mongo in their names or their descriptions):
dpkg -l | grep mongo
In summary, I would do (to purge all packages that start with mongo):
sudo apt purge mongo*
and then (to make sure that no mongo packages are left):
dpkg -l | grep mongo
Of course, as mentioned by @alicanozkara, you will need to manually remove some directories like /var/log/mongodb and /var/lib/mongodb
Running the following find commands:
sudo find /etc/ -name "*mongo*" and sudo find /var/ -name "*mongo*"
may also show some files that you may want to remove, like:
/etc/systemd/system/mongodb.service
/etc/apt/sources.list.d/mongodb-org-3.2.list
and:
/var/lib/apt/lists/repo.mongodb.*
You may also want to remove user and group mongodb, to do so you need to run:
sudo userdel -r mongodb
sudo groupdel mongodb
To check whether mongodb user/group exists or not, try:
cut -d: -f1 /etc/passwd | grep mongo
cut -d: -f1 /etc/group | grep mongo