[Discuss] Fedora 28 Doesn't See External DVD Drive on USB Port

[David Kramer]

I doubt the solution to that other person's problem is the same one you
are having, but it's possible.  Let me explain it in more detail,
because it actually has nothing to do with external DVD drives
specifically, which is muddying the waters.

These days, most storage devices emulate the old SCSI (Small Computer
System Interface) standard at the API level. That is, the hardware is
different, but the commands that an OS or BIOS would send to an old SCSI
drive.  That's why the devices are named /dev/sda, dev/sdb, etc.  The
devices are named in order as they are discovered, so the main drive is
/dev/sda, and if you have a second disk it would be /dev/sdb.

Partitions are named by appending the partition number to the device
they are on.  The first partition on the first device is /dev/sda1, and
the second partition would be /dev/sda2.

Let's say you plug in a thumb drive after that.  That would be the third
disk, so it would be /dev/sdc.   If you then plugged in your external
DVD drive, it would probably be /dev/sdd.  That all works pretty well.

Here's the problem: Let's say you have some configuration file, whatever
it is, that refers to a disk, because you have a second hard drive in
your computer.  let's call it /dev/sdb.  Now let's say you plug in your
external DVD player and it comes up as /dev/sdc, and all is right with
the world.

BUT: If you remove that second drive from your computer and there is no
longer a /dev/sdb, and you do not update that configuration file, then
when you add your external DVD player, it will come up as /dev/sdb
instead.  That configuration file is telling your computer that /dev/sdb
is something else.  And there we have the problem.

Now this file in particular, /etc/fstab (and you need to use sudo to
edit it) tells the computer what each drive is for and how to mount it
and to where.  It is a BAD file to have incorrect information in for
that reason, and that is the problem described in your mail.  I doubt
that's your problem, but if you send us the contents of that file, we
may be able to confirm.

Some good news: There IS a better way. Partitions can also be identified
by user-specified labels, and that eliminates the whole
who-got-connected-first problem. It also lets you set up rules, like
automatically mounting THIS particular external USB device, but not this
other one.

Hope that helps.


On 12/29/18 10:12 PM, Nancy Allison wrote:
> Thank you, Dan.
>
> You've provided some details that I can follow, but I am not well enough
> grounded to know how I would use them. (For example, I have no idea where
> fstab lives or how I get to it.) If I can find someone to help me out
> painstakingly, with a generous donation of their time and effort, I (they,
> really) can undoubtedly fix the problem. I may wait until the next
> InstallFest for help.
>
> But this leaves me wondering, can it really be that everyone using Fedora
> 28 struggles along with this same problem that obviously affects plenty of
> people? CDs and DVDs are not used as much as they once were, but they are
> still in use. If you google "fedora 28 doesn't recognize external dvd
> drive" you get people struggling with this back in 2010 and 2011. Is this
> what Fedora is like -- everyone struggles with problems individually? And
> you really have to have a lot of technical knowledge to deal with these
> problems as they come up. Maybe Fedora is just too tecchie for me, but it
> seems as if Ubuntu was, too, when I used it before Fedora. Maybe Red Hat is
> easier for a non-technical person to handle?
>
> Just thinking out loud. Thanks for the additional info.
>
> On Sat, Dec 29, 2018 at 7:12 PM Dan Ritter <dsr at randomstring.org> wrote:
>
>> Nancy Allison wrote:
>>> Hi, all.
>>>
>>> When I plug in my external disk drive into my Fedora 28 machine, it does
>>> not show up in Nautilus.
>>>
>>> I go looking online, and, sure enough, this problem has occurred for
>> plenty
>>> of people for 5+ years over many releases of Fedora.
>>>
>>> I find a discussion in which someone evidently solved the problem. Here
>> is
>>> what the person reported:
>>>
>>> "NVM - found the cause. Old entry in fstab for a second swap not present
>> on
>>> sdb1 and first USB disks being assigned sdb. Cleaned that up and now all
>>> drives plugging correctly.
>>> Willtech ( Sep 23 '18 )"
>>>
>>> How do I apply this information? Where is fstab? When does a first swap
>>> occur? When does a second swap occur? What does it mean to be assigned
>> sdb?
>>
>> /etc/fstab consolidates mounting information.
>>
>> Each active line defines:
>>
>> <file system> <mount point>   <type>  <options>  <dump> <pass>
>>
>> For example:
>>
>> /dev/scd0   /media/cdrom0   ISO9660     ro      1   1
>>
>> device/partition name, then where you want it mounted, then the
>> type of filesystem.
>>
>> If you have a single disk called /dev/sda, for instance, you
>> might see your external CD show up as /dev/sdb. If there's
>> already a /dev/sdb listed in the file, that will conflict.
>>
>> Hope that helps.
>>
>> -dsr-
>>
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