我正在尝试安装httpie：
» sudo apt update
Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://archive.ubuntu.com/ubuntu bionic-security InRelease
Hit:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
» sudo apt install httpie
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package httpie 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 'httpie' has no installation candidate
但包裹是上市
其他包也会发生这种情况：
E: Unable to locate package git-annex
E: Package 'httpie' has no installation candidate
E: Unable to locate package jshon
E: Unable to locate package python-pip
E: Unable to locate package tree
但它们也存在：
到底是怎么回事？
这是我的sources.list：
» cat /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu bionic main
deb http://archive.ubuntu.com/ubuntu bionic-security main
deb http://archive.ubuntu.com/ubuntu bionic-updates main
这是我的系统：
» lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic
编辑
这是一个 ubuntu 服务器系统，没有 GUI。