[FS#741] RB750r2 sysupgrade cant unmount Resource busy error

[LEDE Bugs]

The following task is now closed:

FS#741 - RB750r2 sysupgrade cant unmount Resource busy error
User who did this - Mathias Kresin (mkresin)

Reason for closing: Not a bug
Additional comments about closing: The error messages are harmless. Especially they occur after the reboot and everything works for you.

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=741