gpg --gen-key: Not enough random bytes available

用gpg工具生成密钥时，提示随机字节数不够
Not enough random bytes available. Please do some other work to give the OS a chance to collect more entropy! (Need ### more bytes)
We need to generate a lot of random bytes. It is a good idea to perform some other action (type on the keyboard, move the mouse, utilize the disks) during the prime generation; this gives the random number generator a better chance to gain enough entropy.

• 情况分析

  运行此命令的设备是 AWS 上申请的一台EC2虚拟机，安装的是 Ubuntu 16.04.2 LTS，使用SSH客户端远程管理服务器。
  根据提示，可采取一些动作（action）生成更多的随机字节（random bytes），如敲击键盘、移动鼠标、使用硬盘等等。因 SSH 链接只能使用键盘，所以采取敲击键盘和下载大文件两个方法，但都不奏效，gpg 工具仍不能返回任何结果。

• 解决办法

  在 stackoverflow 上看到一篇 closed 状态帖子，找到了解决问题的办法

  • 可用

    sudo apt-get install rng-tools

    I have found a remarkable speed increase by using rng-tools in the universe repository, which can be installed with Synaptic or another GUI package manager, or via the command-line

  • 未试

    sudo find / -type f | xargs grep somerandomstring > /dev/null

    Executing the following command in the background works for me

• 参考链接

  [1] Amason webservices homepage
  [2] A stackoverflow post