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

[LEDE Bugs]

The following task has a new comment added:

FS#741 - RB750r2 sysupgrade cant unmount Resource busy error
User who did this - Francis (francisuk1989)

----------
Thanks Mathias :) 

was just getting abit worryed when it says

Appending jffs2 data from /tmp/sysupgrade.tgz to firmware..
.File /tmp/sysupgrade.tgz does not exist
umount: can’t unmount /dev/pts: Resource busy
umount: can’t unmount /dev: Resource busy
umount: can’t unmount /tmp: Resource busy
umount: can’t unmount /: Invalid argument
----------

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=741#comment2521