ubuntu出现如下错误：
{
Welcome to Ubuntu 16.04.5 LTS (GNU/Linux 4.15.0-42-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
77 packages can be updated.
0 updates are security updates.
*** System restart required ***
Last login: Fri Dec 7 13:59:33 2018 from 10.12.21.2
-bash: ls: No such file or directory
-bash: lesspipe: No such file or directory
-bash: dircolors: No such file or directory
-bash: ls: No such file or directory
carrie@carrie-MMLP7AP-V7:~$ sudo su -l
Command ‘sudo‘ is available in ‘/usr/bin/sudo‘
The command could not be located because ‘/usr/bin‘ is not included in the PATH environment variable.
sudo: command not found
}
原因是：
默认的环境变量错误，
#cat /etc/profile
export PATH=
修改错误:
# export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin
# reboot
重启机器，登陆OK。
-bash: ls: No such file or directory 错误的原因及解决办法
原文：https://www.cnblogs.com/carriezhangyan/p/11841003.html