Show only upper directory usage inside docker running in kubernetes-CodePudding

My project will run clients' (docker) containers with kubernetes. And the command df -h inside docker container will show the host / usage like this:

root@aggregator-demo-vgpovusabzqf-578f547cc5-rc8g6:/# df -h
Filesystem                         Size  Used Avail Use% Mounted on
overlay                            1.8T  227G  1.5T  14% /
tmpfs                               64M     0   64M   0% /dev
tmpfs                              252G     0  252G   0% /sys/fs/cgroup
/dev/mapper/ubuntu--vg-ubuntu--lv  1.8T  227G  1.5T  14% /etc/hosts
shm                                 64M     0   64M   0% /dev/shm
tmpfs                              504G   12K  504G   1% /run/secrets/kubernetes.io/serviceaccount
tmpfs                              252G     0  252G   0% /proc/acpi
tmpfs                              252G     0  252G   0% /proc/scsi
tmpfs                              252G     0  252G   0% /sys/firmware

which is not quite helpful for user to understand how much storage already used. And I see some container platforms which can show only the actually user usage like this:

root@container-bc574b56:~# df -lh
Filesystem      Size  Used Avail Use% Mounted on
overlay          25G  574M   25G   3% /
tmpfs            64M     0   64M   0% /dev
tmpfs           378G     0  378G   0% /sys/fs/cgroup
shm              40G     0   40G   0% /dev/shm
/dev/sdb        150M  4.0K  150M   1% /init
tmpfs           378G   12K  378G   1% /proc/driver/nvidia
/dev/sda2       219G   26G  184G  13% /usr/bin/nvidia-smi
udev            378G     0  378G   0% /dev/nvidiactl
tmpfs           378G     0  378G   0% /proc/asound
tmpfs           378G     0  378G   0% /proc/acpi
tmpfs           378G     0  378G   0% /proc/scsi
tmpfs           378G     0  378G   0% /sys/firmware

The / directory shows Avail is 25Gi which is the actual container limitation and the Used is 574M which is the docker upper directory usage. How to implement like this? Maybe this is not the capability of docker and it may use some other implementation?

CodePudding user response：

df simply queries the filesystem for available space.

If you're using the standard overlay2 driver, the container filesystem is just a view onto the host filesystem; there's no way for df to provide a container specific value because there is no separate filesystem.

If you're using something like the devicemapper, zfs, or btrfs storage drivers, then each container has its own unique filesystem, so df can provide information that is specific to the container.