All of a sudden all disk space has been consumed on my VPS running MailCow. The df-u command gives me:
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2       196G  186G     0 100% /
devtmpfs        3.9G     0  3.9G   0% /dev
tmpfs           3.9G     0  3.9G   0% /dev/shm
tmpfs           3.9G  370M  3.5G  10% /run
tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/sda1       969M  221M  683M  25% /boot
overlay         196G  186G     0 100% /var/lib/docker/overlay2/7a35243a58e3c6655021832ac194f9a026567ae953218eecff92a6a33d19972f/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/7f2ea3b876fe5704aa53679e51be39b48d51570e3b1bbdcb89d6b84166eb7743/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/39ffdfbac11286c4cf9e125d30a4fab7db1c83575eb1aee0b4e3eb7c49ef7597/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/58afcfcb60b623147a3e015b45bc297a1a606bb07129a7e9900b2c64fc32982b/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/a20d5eee3a5ef8c359e7664e814f09e6abb3068c93c64bd8b9b1f209d8435ca6/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/0b0abf184bf321f2a776839fef1fdfdc49f4abceb42f7c50a6caac0ae698006e/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/626c444134e3f29bcf560617ef9c0110ebbd6aef12a1fe0f69845650f80b3194/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/f211af52d86d7975a6fa2c2babeba0489db85b319ca571dabb592532ddae0be1/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/90d9b5a91b182162b83204a97a8e17b2333fd9374e7c6f92ad942b68c5357e0d/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/7f35c8cd95352e778729fb80a639c506923b8790147dba32d1ef33f65dedc6bc/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/1235d404ca80d6550d31a2dd49350edd9dcbb2bfc274cb00adf2fbdf662c5f11/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/198835ed772a149edd7180a00fb1f70492cbac4c6a8bf2e889a3fede3e668962/merged
overlay         196G  186G     0 100% /var/lib/docker/overlay2/6119c3228ccdc1ffed9fa38952649cbdd6081f3ee74f785729dde440b51addbe/merged
shm              64M     0   64M   0% /var/lib/docker/containers/3de7558b152e2d1cbb08387e799bf32bdbba38b33fff2d20a8710b0a907d7870/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/19fdc25f519a62a241e1ed95d19359621118a1fe979b802ca82181204f7ce4cc/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/80694d06d0d02b350b0c415753f562c2c05747eba7d9559aaafd5518635b8d85/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/9756f8004e9454180f001c0ac71067f3d40ecf89b84b7fcfcf61becc5dd23ab9/mounts/shm
shm              64M  8.0K   64M   1% /var/lib/docker/containers/4911bfb10e3fd4fd8895a4e633efa3a0a5f6d33f0ebc622135b179537ed5f297/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/8f9785d5468b59e3d77ee6aa946ef095676d547577f7b827cf9f0ddc2a502b05/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/373ee1752e78060ea7bbd3e72abb01937a90c5206a309073a31738276d760454/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/0bf8c3d2e407d90b43a76e56e838f056d9a478db1dae102322342a5c5f61fafc/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/3c57c7911f75a328d1c42395414a90dc0eb0438071f29e64e14a90246794c2fb/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/19b911d665bf0425ada0911a0db4c51e2c58d0cf2810b2cbcb79d75e5e32221f/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/51d27d192f9e7963ea99194ccb8a85195377d16f3bea76c51d7150a566ea186a/mounts/shm
shm              64M     0   64M   0% /var/lib/docker/containers/a13feb271d6324ba0006d4f17070e5ce8f93ac99820e2384fcafa450881b704e/mounts/shm
overlay         196G  186G     0 100% /var/lib/docker/overlay2/83f2163bd57cb0841abab6c90ff61362669acad2eabc343e4155bae9b66c7090/merged
shm              64M  8.0K   64M   1% /var/lib/docker/containers/7a9b523eb21f6be3b390707b39b222f2f790f716726979fd6dd1c10b165f2893/mounts/shm
overlay         196G  186G     0 100% /var/lib/docker/overlay2/898d560b1f067c22c64e465be3d5e2b91de42d8771d4316d48b66e72f7c333cf/merged
shm              64M     0   64M   0% /var/lib/docker/containers/dbaab9f6870ae55349b556b3bafc3c14706b3ef8336da55842b4fbd700e7f6ee/mounts/shm
overlay         196G  186G     0 100% /var/lib/docker/overlay2/42efe03fbf7189fa77eb15cba23226f6ee97bb2c28e1d3168db33794fab08b2f/merged
shm              64M     0   64M   0% /var/lib/docker/containers/22784a761ed55c0d2e549181ea2e15778758cd34a79d7735a7290862a5d5e746/mounts/shm
shm              64M   12K   64M   1% /var/lib/docker/containers/73166e41a4ccaf89629109d8d897fa9a4ef33daa466b7f68d586aefaf6bd2f84/mounts/shm
overlay         196G  186G     0 100% /var/lib/docker/overlay2/9688b1efd24ff111c15f6285e905be6bce40ca73b694752b5bf541451bd8db4d/merged
shm              64M     0   64M   0% /var/lib/docker/containers/0a3b53a9ebe5e2eaa5d45778aae4019c7573de6f9eba5928c9ab109dffc2e475/mounts/shm
tmpfs           783M     0  783M   0% /run/user/0
I have tried docker system prune - but it did not give me much…
Any hints on how to proceed from here ?
Regards
Brian