如果我构建映像并且一段时间不使用它，那么映像将被自动删除。例如。当我发出docker images时，没有这样的图像。 Here is same issue，解决方案是至少有100GB的可用空间。我只有4GB的免费cca。是否可以设置一些限制以防止自动删除图像？
wakatana@ubuntu:~$ cat /etc/os-release
NAME="Ubuntu"
VERSION="18.04.3 LTS (Bionic Beaver)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 18.04.3 LTS"
VERSION_ID="18.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=bionic
UBUNTU_CODENAME=bionic
wakatana@ubuntu:~$ uname -a
Linux ubuntu 4.15.0-88-generic #88-Ubuntu SMP Tue Feb 11 20:11:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
wakatana@ubuntu:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.3 LTS
Release: 18.04
Codename: bionic
wakatana@ubuntu:~$ docker --version
Docker version 19.03.5, build 633a0ea838