正如所描述的http://ubuntu.com/blog/ubuntu-core-in-lxd-containers，Ubuntu 核心可以通过以下方式安装http://snapcraft.io/lxd通过执行lxc launch images:ubuntu-core/16 ubuntu-core。本教程已过时，因为最新版本的Ubuntu 核心看起来是 20 而不是 16，所以我执行了lxc launch images:ubuntu-core/20 ubuntu-core，但它没有完成应该做的事情。该怎么办？
$ lxc launch images:ubuntu-core/20 ubuntu-core
Creating ubuntu-core
Error: Failed instance creation: Failed getting image: Failed parsing
stream:
Get "https://uk.images.linuxcontainers.org/streams/v1/index.json": x509:
certificate has expired or is not yet valid:
current time 2021-09-01T15:42:30+01:00 is after 2021-09-01T12:00:00Z