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docker with no volume running, where does container system file store?

If I run a container with no volume specified, where does container system file store ?

  • docker run -it c_name i_name:tag

when I run a container without volume, only container folder created in /var/lib/docker/container, but I If I create a large file in container file system, where does it stored on host? Because I want to know if it will cause occupying disk size issue.

Solution

  • The container's storage is composed of different layers, different layers will finally form a merged layer.

    Let's make a small experiment next:

    1. Start a container & setup a new file:

    # docker run -idt --name trial debian /bin/bash
# docker exec -it trial /bin/bash
root@e6c2b6336753:/# echo "helloworld" > test.txt
root@e6c2b6336753:/# cat test.txt
helloworld

    2. Find the merged storage layer id:

    # docker inspect --format=" {{ .GraphDriver.Data.MergedDir }} " trial
/var/lib/docker/overlay2/8f2e14d33448cb83e581b2950a69faa827a012904051c845abf550273196f90f/merged

    Here, 8f2e14d33448cb83e581b2950a69faa827a012904051c845abf550273196f90f is the layer id.

    3. Check layer:

    # cd /var/lib/docker/overlay2/8f2e14d33448cb83e581b2950a69faa827a012904051c845abf550273196f90f/merged
root@shlava:/var/lib/docker/overlay2/8f2e14d33448cb83e581b2950a69faa827a012904051c845abf550273196f90f/merged# ls
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  test.txt  tmp  usr  var
root@shlava:/var/lib/docker/overlay2/8f2e14d33448cb83e581b2950a69faa827a012904051c845abf550273196f90f/merged# cat test.txt
helloworld

    So, as a conclusion, you could see from above, the file system contents could be found in /var/lib/docker/overlay2/ with layer id as folder, you could check the disk there.