Ubuntu 服务器 18.04 试过：
~$ sudo apt-get update
Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease
Get:2 http://archive.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Get:4 http://archive.ubuntu.com/ubuntu bionic/main Translation-en [516 kB]
Get:5 http://archive.ubuntu.com/ubuntu bionic-security/main Translation-en [78.1 kB]
Get:6 http://archive.ubuntu.com/ubuntu bionic-updates/main Translation-en [161 kB]
Fetched 927 kB in 1s (628 kB/s)
Reading package lists... Done
:~$ sudo apt-get install krb5-kdc krb5-admin-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package krb5-kdc is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'krb5-kdc' has no installation candidate
E: Unable to locate package krb5-admin-server
Ubuntu 文档有：
sudo apt install krb5-kdc krb5-admin-server
结果相同。
有一篇关于 Ubuntu 14 的旧帖子...更新解决了他的问题，而不是我的问题。
我在 Ubuntu 存储库站点上进行了包搜索，发现 krb5 包的许多位置。
我不知道为什么“标准”存储库不包含它们，但我只是添加了一个存储库，进行了更新，现在它们可以安装了。