What I did before the error:
Code:
$ sudo rsync -a /usr/* /media/4c**********/usr/ ## To backup my /usr directory because my system partition was running out of space
$ su
# export PATH="/media/4c*******/usr/bin:/media/4c*****/usr/sbin:etc:etc:etc:${PATH}" ## So that system searches /media/4c****/usr/* before /usr
# rm -r /usr/* && mount --bind /media/4c*******/usr /usr ## To make space on system partition and then replace /usr with 'external' partition
# exit
$ sudo nano /etc/fstab ## about to make changes persistant but,
sudo: effective uid is not 0, is sudo installed setuid root?
$ su
# apt-get update
......
......
......
Error: GDBus.Error:org.freedesktop.DBus.Error.Spawn.PermissionsInvalid: The permission of the setuid helper is not correct
# apt-get upgrade
.....
.....
..... ## everything went well except like the update
Error: GDBus.Error:org.freedesktop.DBus.Error.Spawn.PermissionsInvalid: The permission of the setuid helper is not correct
What to do?