[Bug 1961085] [NEW] grub-install prints misleading error message

[Oliver]

Public bug reported:

When i try to install grub on an usb stick without root permissions with
the following command line, i get a misleading error message:

[code]
~$ grub-install --recheck --boot-directory=/media/ubuntu-mate/usbstick/boot/ /dev/sda
Installing for i386-pc platform.
grub-install: warning: disk does not exist, so falling back to partition device /dev/sda1.
grub-install: warning: disk does not exist, so falling back to partition device /dev/sda1.
grub-install: warning: disk does not exist, so falling back to partition device /dev/sda1.
grub-install: error: disk `hostdisk//dev/sda1' not found.
[/code]

This error message is misleading. The disk does exist. The command works without errors, when i put a sudo in front of it.
The error message should be something like:

"You need to be root to have write access"

There should be a check if grub2 does have write access and if it
doesn't, the error message should  tell the user, that he doesn't have
permissions and should change to root or use sudo.

This was tested on Ubuntu 21.10

** Affects: grub2 (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: access error grub-install grub2 message misleading permissions root write

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https://bugs.launchpad.net/bugs/1961085

Title:
  grub-install prints misleading error message

Status in grub2 package in Ubuntu:
  New

Bug description:
  When i try to install grub on an usb stick without root permissions
  with the following command line, i get a misleading error message:

  [code]
  ~$ grub-install --recheck --boot-directory=/media/ubuntu-mate/usbstick/boot/ /dev/sda
  Installing for i386-pc platform.
  grub-install: warning: disk does not exist, so falling back to partition device /dev/sda1.
  grub-install: warning: disk does not exist, so falling back to partition device /dev/sda1.
  grub-install: warning: disk does not exist, so falling back to partition device /dev/sda1.
  grub-install: error: disk `hostdisk//dev/sda1' not found.
  [/code]

  This error message is misleading. The disk does exist. The command works without errors, when i put a sudo in front of it.
  The error message should be something like:

  "You need to be root to have write access"

  There should be a check if grub2 does have write access and if it
  doesn't, the error message should  tell the user, that he doesn't have
  permissions and should change to root or use sudo.

  This was tested on Ubuntu 21.10

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