Ubuntu 18.04 登录循环和命令无法找到

Question

在我启动系统后，我陷入了登录循环。通过终端登录后，许多命令（如“ls、sudo……”）不起作用，并显示：

the command could not be located because '<path of the command>' is not included in the PATH environment variable

我这样做后这个问题就解决了source ~/.bashrc，source /etc/environment但我仍然不知道如何登录