描述

在使用 Devstack 的时候需要时常切换用户su stack，此时会触发错误：

root@mickeyfan-dev:~# su stack
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied
bash: /dev/null: Permission denied

一般而言，Permission denied 问题可以通过 reset 权限 chmod 666 /dev/null 来解决，但在 Ubuntu 中，系统会自动将设备的权限还原为 420 crw--w---- 1 root tty 1, 3 Aug 26 11:46 /dev/null。所以常用的方法并不能解决该问题。

解决方案

此时，你需要删除 /dev/null 文件，并重新创建它：

rm -f /dev/null; mknod -m 666 /dev/null c 1 3