环境：docker上安装的ubuntu20。但是无妨，当做ubuntu即可

上课需要，老师让我们安装mongodb-org，给了一个TXT指南，如下：

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git checkout origin/06.06-writing-to-mongodb
apt install gnupg
curl -fsSL https://www.mongodb.org/static/pgp/server-4.4.asc | apt-key add -
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.4.list
apt update
apt install mongodb-org
mkdir -p /data/db
screen mongod

~To test~
mongo issuetracker --eval "db.employees.remove({})" 
node scripts/trymongo.js
mongo issuetracker scripts/init.mongo.js
 

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但是在multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.4.list 这一行会显示no such directory。以及后面mongodb-org会失败，会出现 E: Unable to locate package mongodb-org

我搜索了一些文档，都失败了。。比如，虽然可以安装mongodb，方法是apt install mongodb，但是这个是ubuntu系统的一个非官方的mongodb，官方版本的额需要-org那个版本的才行。

之后尝试其他博主的方法还遇到如下错误，大家可以参考一下： 

mongodb-org : Depends: mongodb-org-shell but it is not going to be installed
               Depends: mongodb-org-server but it is not going to be installed
               Depends: mongodb-org-mongos but it is not going to be installed
               Depends: mongodb-org-tools but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

The following packages have unmet dependencies:
 mongodb-org-mongos : Depends: libssl1.0.0 (>= 1.0.1) but it is not installable
 mongodb-org-server : Depends: libcurl3 (>= 7.16.2) but it is not installable
                      Depends: libssl1.0.0 (>= 1.0.1) but it is not installable
 mongodb-org-shell : Depends: libssl1.0.0 (>= 1.0.1) but it is not installable
 mongodb-org-tools : Depends: libssl1.0.0 (>= 1.0.2~beta3) but it is not installable
E: Unable to correct problems, you have held broken packages.

然后我尝试安装libssl4。。都没有效果

最后是在ubuntu 16.04上安装mongodb时出错-Java 学习之路

我先是按照他的要求删除了所有相关的东西。然后按照官方的要求进行了安装。很顺利，成功了！原来问题是：老师给的安装方案，可能和我的ubuntu20版本可能不匹配。。。。。。