Trying to use pre-hooks scripts to cleanup the filesystem of unwanted files like:

find /$ZREPL_FS -type d -name ".thumbnails" | xargs -n 1 rm -rf

I kept getting Read-only filesystem error

IMO the docs should mention:

sudo mkdir -p /etc/systemd/system/zrepl.service.d/
cat <<EOF | sudo tee /etc/systemd/system/zrepl.service.d/override.conf >/dev/null
[Service]
ProtectSystem=off
#ProtectHome=off
EOF