I have a volume mounted in a container. The volume is of fixed size and the container writes data to this volume. How can I check the space left on the volume from within the container.
I can run commands on host running docker, but is it possible to do this from inside the container where the volume is mounted?
You can basically get the capacity as you would do in a normal Linux machine: df -h executed inside the container:
Prerequisite A: create a fixed size volume
docker volume create --driver local --opt type=tmpfs --opt device=tmpfs --opt o=size=100m,uid=1000 fixed-size-volume
Prerequisite B: Mount the volume in your container wherever you need you mountpoint to be (/var/fixed-mount-point in my example)
docker run -it --rm --mount source=fixed-size-volume,target=/var/fixed-mount-point alpine sh
Step 1: List the mounts inside the container and filter by the name of the mount point(I am already with a terminal inside my container since I used -it. To open a terminal you can use docker exec -ti <containerID> sh
/ # df -h | grep fixed
tmpfs 100.0M 0 100.0M 0% /var/fixed-mount-point
Step 2: Create a dummy file in the mount point: I used dd to create a 1MB file
dd if=/dev/zero of=/var/fixed-mount-point/file.txt count=1024 bs=1024
Step 3: Check again the capacity of the volume. Note the change from 0% to 1%
/ # df -h | grep fixed
tmpfs 100.0M 1.0M 99.0M 1% /var/fixed-mount-point