I am running a bunch of Docker containers in a Linux virtual machine. At some points, I had some memory errors, and had to remove unused containers and images using the pruning command: sudo docker system prune --all

Now, when I run the command sudo df -h, here is the output:

Filesystem      Size  Used Avail Use% Mounted on
udev             14G     0   14G   0% /dev
tmpfs           2.8G  1.6M  2.8G   1% /run
/dev/sdb1        29G   24G  5.7G  81% /
tmpfs            14G  358M   14G   3% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            14G     0   14G   0% /sys/fs/cgroup
/dev/sdb15      105M  6.6M   98M   7% /boot/efi
/dev/sda1       173G   61M  164G   1% /mnt
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/80835ecbaca2bc94bc2fd159a9d39ec61a66f6aee4db559ba7ab79fc3b2844e9/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/f6d92a722c1c64fefb6b0841c80003d847b305d11c5690578e5a0b8205138b9f/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/f7c5b5edbb37f7117933ee1bcad12fd65b160a779248a51c1c085c6a816e55aa/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/03687a08b0848235e38c47c782b15f6f84b722661cb24404f097d1576a1eedb5/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/a29f888c77d541b341107357219c4ec454c796f856887de3c50c3fc6738ffb44/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/1a939bb07d6b3df8d1731f79ec5740aab5f59e33177af4a7ef85081af82c50f0/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/1aa1ca3c7e65ff84d55e114b6bf077c6f5c7692874103160e3d9638d3c54e3ec/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/1bf6e7a2b9332faf760eaf98fc87d8e49eafbbebf2e3e725c87c1bd0020037b3/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/664eccc5235ce430b9d13f03c8db02899c46a9d52c5804c6b86847b27afae478/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/df88af21d2cc95570f07fc750d40f1154371918097ca781ebccc686ea9d2a1ea/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/f6d17a19e6675fb30e6fd8c62675216da898505648353d56b314337301c5e9c2/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/d3ae8ed3dd66051a3c7924d49c0f71853b87cf0c942873f453610dcda1f9255d/merged
overlay          29G   24G  5.7G  81% /var/lib/docker/overlay2/025d66cc397fffdcbfacbf5cee25b2ccf8421321ed744669e35b596b0f522be6/merged
tmpfs           2.8G     0  2.8G   0% /run/user/1000

As you can see, Docker overlay folders take A LOT of memory. Also, I find it weird that there are 13 overlay folders that take the exact same amount of disk space.

My question: How can I clean it?

Note that I don't want to stop the running containers. All I want to do is delete folders that are not used anymore.