1. 问题

2. 删除bash并重新安装

删除：

sudo rm /bin/bash

（https://blog.csdn.net/u011128515/article/details/22896837）
再安装：

bash文件电脑中是有下载的deb文件的，按上图路径找到了并下载了出来

ar t bash_4.4.18-2ubuntu1.2_amd64.deb

ar p bash_4.4.18-2ubuntu1.2_amd64.deb data.tar.xz | xzcat | tar xvf - ./bin/bash

将文件进行移动：
sudo mv bash /home/lt/Desktop/bash/bin/bash /bin/

参考：

https://www.cnblogs.com/gdut-gordon/p/12048143.html

https://blog.csdn.net/u011128515/article/details/22896837

https://unix.stackexchange.com/questions/399630/bash-was-overwritten-using-dash-apt-get-reinstall-install-bash-returns-an-er

新用户指定到/bin/bash：
https://blog.csdn.net/qq_42580577/article/details/88907653?utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromMachineLearnPai2%7Edefault-3.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromMachineLearnPai2%7Edefault-3.control