rootstrap：找不到命令

我正在尝试创建一个系统根来使用监狱进行一些测试，并且我正在尝试安装rootstrap whitout 成功。

$ rootstrap
rootstrap: command not found

尝试安装时：

$ sudo apt-get install -y rootstrap
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package rootstrap

我的操作系统版本：

                    ./+o+-       
                  yyyyy- -yyyyyy+      OS: Ubuntu 20.04 focal
               ://+//////-yyyyyyo      Kernel: x86_64 Linux 5.4.0-33-generic
           .++ .:/++++++/-.+sss/`      Uptime: 13h 40m
         .:++o:  /++++++++/:--:/-      Packages: 2190
        o:+o+:++.`..```.-/oo+++++/     Shell: bash 5.0.16
       .:+o:+o/.          `+sssoo+/    Resolution: 1920x1080
  .++/+:+oo+o:`             /sssooo.   DE: Xfce
 /+++//+:`oo+o               /::--:.   WM: Xfwm4
 \+/+o+++`o++o               ++////.   WM Theme: Qogir-win-dark
  .++.o+++oo+:`             /dddhhh.   GTK Theme: Qogir-win-dark [GTK2]
       .+.o+oo:.          `oddhhhh+    Icon Theme: Qogir-ubuntu-dark
        \+.++o+o``-````.:ohdhhhhh+     Font: Noto Sans 9
         `:o+++ `ohhhhhhhhyo++os:      Disk: 17G / 156G (11%)
           .o:`.syhhhhhhh/.oo++o`      CPU: Intel Core i7-4790K @ 8x 4.6GHz [28.0°C]
               /osyyyyyyo++ooo+++/     GPU: GeForce GTX 1060 6GB
                   ````` +oo+++o\:     RAM: 5672MiB / 15919MiB

这个包是另一个包的替代品吗？