从 18.04 升级到 20.04 后，我注意到关机或重新启动期间出现几个警告，例如：
Failed to unmount /oldroot: Device or Resource busy
Failed to unmount /oldroot/dev/pts: Device or Resource busy
Failed to unmount /oldroot/dev: Device or Resource busy
Failed to unmount /oldroot/sys: Device or Resource busy
有时它在屏幕上可见，有时它被飞溅覆盖。
我找不到任何与使用journalctl或日志相关的内容，我唯一发现的是：
abr 23 22:24:36 vanburen07-G5-5590 sudo[6451]: vanburen07 : TTY=pts/0 ; PWD=/home/vanburen07 ; USER=root ; COMMAND=/bin/umount /oldroot/dev/pts
fstab 中没有任何具体内容：
<file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/nvme0n1p3 during installation
UUID=063c6892-66d6-4598-9dcf-82136ad4ea81 / ext4 errors=remount-ro 0 1
# /boot/efi was …