Having installed my ManjaroOS on my hard disk. If I boot my computer with an USB live system stick, how can I edit the original grub file on my hard disk in case of a crash for repairing it in case needed?
update-grub
has to be a separate command - not on the same line as written in the OP
but only after it has been verified that the chroot has actually worked
this is not a command
it is two commands - does not work this way
that might partially work
You probably want to use manjaro-chroot instead of plain chroot
(it takes care of all the things you have to do manually to actually be able to successfully use your chroot)
check and verify that that will put you into your system, mounted there
if it did (it’s likely)
then you can do things like:
editing /etc/default/grub
and
running update-grub