CDROM not recognised/opening after install

**mr_ed** · 02-19-2005, 10:25 AM

Victor, I'm sorry I couldn't get back to you last night. I know it's frustrating to try a couple of things, then wait a day, try a couple of things, wait two days....

Knoppix-installer made four entries in my /etc/fstab: 3 CD (1 audio) and 1 DVD, for a single CD/DVD drive. No other Linux has given me four. So that's a known quirk.

I suspect one of the problems is the transition from 3.4 to 3.6 kernels - 3.4 has one way of dealing with CD drives, and 3.6 adds another, and Knoppix lets you choose either kernel. So extra entries in /etc/fstab and /mnt may be there to cover all the possibilities. And to add confusion!

It might help to know which kernel is running. Find out with

$ uname -r

The uname command tells you a few tidbits about your system. Usa -a to see all the tidbits (none of the others should be relevant right now) and -h to see what all the pieces are.

And yes, knowing that the drive is working in another environment is important diagnostic info. I'm sorry, I forgot whether you know where it's physically wired in your computer. Are there other optical drives?

When the computer first powers on, the BIOS looks for drives and (by default, anyway) displays what it sees. The bootloader has to start with what the BIOS tells it, so if you have to troubleshoot back to that point, check the BIOS printout. It includes four IDE slots:

- primary master
- primary slave
- secondary master
- secondary slave

If you have one hard drive and one CD (that isn't a true SCSI drive), the standard places for them are HD at primary master and CD at secondary master. I've seen screwy setups, though.

To investigate the mount errors, it will help to know all the identities that Linux has assigned that one drive. If it's in the secondary master position, it might be known as some variation on hdc.

Knoppix gave me all of these mount points for one drive:

- /cdaudio
- /cdrom
- /dvd
- /mnt/cdaudio
- /mnt/cdrom -> /mnt/auto/cdrom
- /mnt/cdromhdc -> /mnt/auto/cdromhdc
- /mnt/dvd
- /mnt/sr0

Note that the link targets /mnt/auto/cdrom and /mnt/auto/cdromhdc don't actually exist on my system!

Putting mount points in the root directory is an annoying thing that Debian does. The sr* name is sometimes given to IDE CD drives.

It would also help to know all the device names that Linux is batting around internally. This isn't really possible, though, because by default Linux populates /dev with billions and billions of entries that might possibly be needed some day under one of the infinitely many situations where it gets installed.

But we can see what's been symlinked to what. To get a shorter list (that will include stuff besides your CD), type this:

$ ls -l /etc | grep "lr"

Here we're taking the output of ls and piping it to grep, which pulls out only the lines containing lr (like symlink lines, which start with those two characters).

You might see, as I did:

- cdaudio -> /dev/cdrom
- cdrom -> /dev/hdc
- cdromhdc -> scdhdc
- dvd -> /dev/cdrom
- sr0 -> scd0 ... and so on through sr16 -> scd16

By themselves these lists of mount points and devices probably aren't useful - except to show that no attempt was made to organize the setup, and so users get to hunt all over the countryside to solve problems. Still, my symlinks that go off into the bit bucket are harmless ... unless Linux is trying to use them!

Now when you get hardware errors you can check what's where by running the commands on the spot. For example,

# ln -s /dev/scd0 cdrom tells you

file exists - but what does that mean?

What the command tries to do is create a new entry (file) in whatever directory you're in. You want this new entry to be called cdrom and to link symbolically to /dev/scd0.

An entry for /dev/scd0 must already exist to create the link, so the error isn't about /dev/scd0 itself.

Is the command telling you that there already is an entry called cdrom in the whatever directory? Is that right? Is it already a symlink to something else?

When you typed

# mount /cdrom

you got a very useless error message. By not specifying both the device and the mount point, you're telling the mount command to go look in /etc/fstab for the other piece.

But something's wrong - see what's actually mounted where with

$ mount

Is something else paired up with /cdrom or /dev/cdrom? What? Where? Are there symlinks that go out into space somewhere?

I'm sorry you're having a problem that's taking so long to track down. I hope I've given you some ideas and tools for looking into this one, but also into other hardware problems that may come up.

Let us know, okay?

-- Ed

**mr_ed** · 02-19-2005, 10:39 AM

Heh - you sneaked in a post while I was writing mine.

I'd say to delete the DVD line from /etc/fstab - it's not doing any good and may be causing this evil. Look for symlinks involving /dev/cdrom, /dev/dvd, /cdrom, and /dvd.

Is sda1 a USB device? If it's working, I'd also clean out the lines "#Added by Knoppix" - if they aren't working, you want to know who to blame, but if they are, then these particular comments are clutter.

-- Ed

**Victor Warner** · 02-19-2005, 01:32 PM

Ed,

Thank you for your detailed replies.

This is the information I got trying to implement what you wrote:

uname -r 2.4.26

uname -a Linux DELL 2.4.26 #1 SMP Sa Apr 17 19:33:42 CEST 2004 i686 GNU/Linux

uname -h comes up as an invalid option

ls -l /etc | grep "lr"
lrwxrwxrwx 1 root root 19 Feb 12 14:01 auto.ftpfs -> /usr/bin/auto.ftpfs
lrwxrwxrwx 1 root root 19 Feb 12 14:01 auto.sshfs -> /usr/bin/auto.sshfs
lrwxrwxrwx 1 root root 10 Feb 12 14:01 init -> /sbin/init

This seems rather different from the list you produced...

ln -s /dev /scd0 cdrom ln: `cdrom': File exists

mount
/dev/hda1 on / type ext3 (rw,errors=remount-ro)
/dev/root.old on /initrd type ext2 (rw)
proc on /proc type proc (rw)
/dev/pts on /dev/pts type devpts (rw)
/proc/bus/usb on /proc/bus/usb type usbdevfs (rw,devmode=0666)
automount(pid389) on /mnt/auto type autofs (rw,fd=4,pgrp=389,minproto=2,maxproto=4)
/dev/hda3 on /mnt/hda3 type vfat (rw)
/dev/sda1 on /mnt/sda1 type vfat (rw)

fstab
I deleted the entry for the DVD and for the entries for "Added by Knoppix" (in fact by commenting these lines out), so that fstab now reads:

# /etc/fstab: filesystem table.
#
# filesystem mountpoint type options dump pass
/dev/hda1 / ext3 defaults,errors=remount-ro 0 1

proc /proc proc defaults 0 0
/dev/fd0 /floppy vfat defaults,user,noauto,showexec,umask=022 0 0
usbdevfs /proc/bus/usb usbdevfs defaults 0 0
sysfs /sys sysfs defaults 0 0
/dev/cdrom /cdrom iso9660 defaults,ro,user,noexec,noauto 0 0
# /dev/dvd /dvd iso9660 defaults,ro,user,noexec,noauto 0 0
/dev/cdaudio /cdaudio iso9660 defaults,ro,user,noexec,noauto 0 0
# Added by KNOPPIX
# /dev/sda1 /mnt/sda1 vfat noauto,users,exec,umask=000 0 0
# Added by KNOPPIX
# /dev/hda2 none swap defaults 0 0
# Added by KNOPPIX
# /dev/hda3 /mnt/hda3 vfat noauto,users,exec,umask=000 0 0

/sda
This is for a USB device and connecting a portable hard-disk/portable music player is recognised as such and I can see the files contained on it.

I am new to Linux so some of what you wrote is still new/unfamiliar.

Victor Warner

**CrashedAgain** · 02-19-2005, 05:40 PM

This is a bug in Knoppix 3.4 that was fixed by version 3.6.
See this: http://www.knoppix.net/forum/viewtopic.php?t=13601
This fix was for a Knoppix-style install which uses the startup script /etc/init.d/knoppix-autoconfig.

For Debian style install which doesn't reconfigure the whole system with each boot I think all you should have to do is 'ln -s /dev/scd0 /dev/cdrom'. You're already on this track but it has to be 'ln -s /dev/scd0 /dev/cdrom' not 'ln -s /dev/scd0cdrom'. If for some reason /dev/cdrom already exists delete it then recreate it as a link to /dev/scd0.

Here's another couple of bugfixes for Knoppix 3.4:

You will get an error about bdflush during the startup. It doesn't affect anything but it's annoying. Here's the fix:

Code:

  
 Comment out this line in checkroot.sh init script: 
 
 (line 35)
 
 vi /etc/init.d/checkroot.sh 
 #[ -x /sbin/update ] && update <--- you add # at the start of this line.

If you have a wheel mouse, you have to change the protocol in /etc/X11/XF86Config-4 from 'auto' to 'IMPS/2':

Code:

Section "InputDevice"
 Identifier  "PS/2 Mouse"
 Driver      "mouse"
 Option      "Protocol" "IMPS/2"

To get your system sounds to work:

Code:

using arts:
Make sure volumes in Kmix are turned up, you need at least master and PCM turned up
KDE controlcenter->enable sounds;turn on system notifications
 /home/user/.KDE/share/config/knotifyrc->set all to true
 configure konqueror->plugins->plugins; enable pipe plugin sounds through arts

One of the reasons I switched to Kanotix is that it didn't have so many little bugs like these. Some of these are still in later versions of Knoppix.

**mr_ed** · 02-20-2005, 12:46 AM

My CD/DVD was dead after installing 3.7 to hard drive this week, so something's still horribly wrong. It may be due to getting ready to try to support non-emulated mode for CDs, new to kernel 3.6.

One of the crazy things knoppix-installer did was create /dev/cdromhdc and a symlink to /mnt/auto/cdromhdc. You can see the logic of it, but that's in addition to other mount points like /cdrom and /mnt/cdrom. And /mnt/auto has nothing in it.

I fixed mine, but we're still working on Victor's.

-- Ed

**mr_ed** · 02-20-2005, 06:37 AM

... transition from 3.4 to 3.6 kernels....

Ummm ... of course I meant 2.4 to 2.6. I doubt I'll be alive when Debian is ready to release 3.6.

uname -h comes up as an invalid option

Why, yes. Clearly I meant uname --help (With two dashes. Ahem.

)

Here's why I made that mistake: Linux commands often can be followed by an argument. Sometimes it's one dash and one letter, sometimes it's two dashes and the whole word, and sometimes either one works. Usually it's not one way with some arguments and the other way with others when there are so few of them.

This seems rather different from the list you produced...

Okay, I'll say it: Just Shoot Me. Try running the command against your /dev directory:

$ ls -l /dev | grep "lr"

automount(pid389) on /mnt/auto type autofs (rw,fd=4,pgrp=389,minproto=2,maxproto=4)

Interesting. I have the /mnt/auto directory, but never get automount there (which has Process ID 389 in your listing).

I deleted ... entries for "Added by Knoppix"

Oops, oops, oops. My bad; my very very bad. Put them back - you want them.

What I meant was that you could delete the lines that were already comments and said, literally,

# Added by KNOPPIX (meaning that the next line was added by Knoppix).

The entries themselves are what you need, the comment as to who put the entries in the table are annoying to me and so I deleted them (the comments). You can leave the comments in, add to them, whatever you like.

But to have your USB, swap, and FAT32 systems automatically mounted at boot time, their entries have to be un-commented. With them commented, you can still mount them manually - that isn't blocked. But that's a pain, so put them back in. I'm sorry!

Okay, like it or not, you're learning Linux!

Commenting out those entries, rather than erasing them, is very good. It doesn't take any more work and lets you recover from bad advice.

Now, the line in /etc/fstab that says:

/dev/cdrom /cdrom iso9660 defaults,ro,user,noexec,noauto 0 0

includes the option noauto, meaning that it doesn't get mounted automatically. That's why it didn't show up in the list you got after running mount. So, to test whether commenting out that DVD line has fixed your problem, try typing either

# mount /dev/cdrom or

# mount /cdrom

For an entry in /etc/fstab, you only need to specify one, and mount will go look up the other. For anything that's not in /etc/fstab (inicluding lines someone shouldn't have told you to comment out), you need to type something like

# mount /dev/cdrom /cdrom

If mount can autodetect the device type, that's all you need. If it can't, it'll complain and you'll need a more complete command like

# mount -t iso9660 /dev/cdrom /cdrom

If you want to specify any options that aren't already included in the /etc/fstab (stuff along the lines of the "defaults,ro,user,noexec,noauto" that you do see) those need to be specified in the mount command too.

Anything that is already mounted can be unmounted with umount.

By the way, the option ro means read-only. Mounting something that you can write to uses rw or, often, mount will automatically decide that it can be mounted read-write (like Linux hard-drive partitions), and then specifying rw isn't necessary. CD drives tend to get mounted read-only by default. (But you can change that in /etc/fstab.)

Also by the way, this entry:

/dev/cdaudio /cdaudio iso9660 defaults,ro,user,noexec,noauto 0 0

is yet another reference to your CD drive. Don't act on the information yet; but do recognize how darned similar it looks to the DVD and CD entries.

Enough for now?

-- Ed

**Victor Warner** · 02-20-2005, 09:29 AM

CrashedAgain,

I tried 'ln -s /dev/scd0 /dev/cdrom' (after deleting /dev/cdrom) and the CD starting working.

However, since I am new to Linux and trying it out stage, I decided to wipe the hard disk amd install version 3.7 and the CDROM now works without any commands and also can play audio CDs as well.

Thank you for your help.

Ed, thank you for your further response, which helps me understand a bit more about how Linux deals with such issues.

Victor Warner