[Bug 500822] Re: /init: line 7: can't open /dev/sr0: No medium found

[Bougron]

Hello

One possible cause may be forgetting duplication of the directory
.disk

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Title:
  /init: line 7: can't open /dev/sr0: No medium found

Status in Ubuntu:
  Confirmed
Status in casper package in Ubuntu:
  Triaged

Bug description:
  Seeing following error message when booting from live installer.

  /init: line 7: can't open /dev/sr0: No medium found

  == Explanation ==

  This continues to affect desktop installers for 17.10 and 18.04.

  There are a variety of underlying causes and the message seen isn't
  related to the cause, which creates immense confusion.

  As soon as the kernel has booted it executes the /init script in the
  /casper/initrd.lz initial ramdisk.

  One of the first things the /scripts/casper functions do is find the
  installer device in order to mount it's file-system. As part of that
  they scan various block devices looking for it, in a repeating loop.
  Each time through the loop existing devices get re-scanned. One device
  that is scanned is the CD/DVD drive, usually /dev/sr0.

  When booting from USB any CD/DVD drive usually has no disc inserted
  and therefore we see repeated

  /init: line 7: can't open /dev/sr0: No medium found

  each time the loop runs.

  There are many reasons why the installer file-system isn't found but
  here is a way to narrow down the cause:

  1. The above message repeats rapidly many times in succession until
  the screen is filled with the same line and eventually it drops to the
  Busybox initramfs shell prompt.

    This means the USB mass storage device wasn't detected, or the
  usb_storage kernel module wasn't loaded by the kernel. This could be
  because the udev rules didn't match the device and therefore didn't
  create the device node (e.g. /dev/sdb)

  2. The above message only appears once, or only repeats after long
  delays, and it takes many minutes to drop to the Busybox initramfs
  shell prompt.

    This indicates the udev daemon is hung whilst processing device
  detection rules, possibly due to it executing an external command
  which has hung. There are some calls to 'udevadm trigger' which has a
  default delay of 120 seconds if the kernel event queue isn't drained -
  which it may not be if some process/task has hung.

  3. The device doesn't present on a device node or path the casper
  scripts look for.

    Setting the kernel command-line option live-media= (e.g: live-
  media=/dev/mmcblk0) which can be supported with live-media-path= (e.g:
  live-media-path=/casper) which is a directory where the live file
  system is, (e.g: by default /casper/filesystem.squashfs)

  There may be other indirect causes of these headline symptoms.

  I've just dealt with one where the UEFI boot failed in this way from a
  USB flash mass storage device. After hours helping the user diagnose
  it, the solution was to move the USB device from the rear USB port of
  the motherboard to a front port!

  Some years ago I had a similar issue on Dell Poweredge servers where
  the CD-ROM device with the installer on was a true SCSI device on a
  SCSI controller, and the installer was not shipped with or loading the
  correct kernel module for that SCSI controller.

  Systems with a Floppy disk controller but no floppy disk attached can
  also cause long timeouts as the FDC ports are probed and a long
  timeout expires before the OS decides there is no FDD attached.

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