Drive detected by kernel, but no /dev entry

demoman · 04-07-2006, 11:49 PM

My USB drive is detected by the kernel: dmesg identifies it as sdc. But...
there is no /dev/sdc entry being created and therefore cannot mount nor fdisk.

Same drive used to work both in this distro and 2 previous ones (Gentoo and SuSE).

I have tried all I could think of (see my initial post for the lengthy details) and read several FAQs on the topic. Abnormal symptoms:

absence of /dev/sdc entries
"Unknown line at line XXXX" returned by lsusb - (what causes this?)
occasional "Attribute {...} does not exist" in /var/log/messages - (what causes this?)

Any suggestion as to how to troubleshoot the problem?

Thanks in advance.

(Sorry for cross-posting this. Initially posted under Ubuntu but not yielding any result and troubleshooting path - if not solution - should be distro-independent).

d0odman · 04-08-2006, 12:43 AM

What have you got creating your dev entries? You can manually make an sdc entry as root, and see if you're able to access your disk that way.

Code:

mknod /dev/sdc b 32 0
mknod /dev/sdc1 b 32 1
mknod /dev/sdc2 b 32 2
mknod /dev/sdc3 b 32 3
... etc

If you use udev, those should automagically appear each time you plug something in, otherwise, you'll have to find out what makes the devices for your system.

demoman · 04-08-2006, 01:55 AM

Thanks for the pointer to udev - making progress!

(mknod procedure didn't work - even after aligning permissions and major number with my SATA drive: mknod -m 660 /dev/sdc1 b 8 1).

But as you pointed out, udev is running the show:

Code:

root@xxxx:/tmp# ls -lR /etc/rc*.d/*udev*
lrwxrwxrwx  1 root root 14 2006-03-24 14:02 /etc/rcS.d/S04udev -> ../init.d/udev
lrwxrwxrwx  1 root root 19 2006-03-24 14:02 /etc/rcS.d/S36udev-mtab -> ../init.d/udev-mtab

I looked into udev-mtab and that lead me to /dev/.static.
While /dev/sdc* are not created, I can successfully mount against /dev/.static/dev/sdc2!
At least now I can access my data.

Code:

root@xxxx:/tmp# mount -t ext3 /dev/.static/dev/sdc2 /mnt/usblin/
root@xxxx:/tmp# ls /mnt/usblin
BACKUPS  lost+found  SYS-BACKUPS

But I'd still like to go to the bottom of this (because I'm also having a problem with my USB printer and suspect it's related).

Do the following errors tell you anything?

Code:

root@xxxx:/tmp# tail -f /var/log/syslog
Apr  7 23:42:34 localhost kernel: [4898405.922000]  /dev/scsi/host14/bus0/target0/lun0: p1 p2
Apr  7 23:42:34 localhost kernel: [4898405.972000] Attached scsi disk sdc at scsi14, channel 0, id 0, lun 0
Apr  7 23:42:34 localhost kernel: [4898405.993000] usb-storage: device scan complete
Apr  7 23:42:44 localhost scsi.agent[16564]: Attribute /sys/devices/pci0000:00/0000:00:10.0/usb1/1-2/1-2:1.0/host14/target14:0:0/14:0:0:0/type does not exist
Apr  7 23:45:52 localhost kernel: [4898603.553000] cm206 cdrom driver $Revision: 1.5 $ can't find adapter!
Apr  7 23:45:52 localhost modprobe: FATAL: Error inserting cm206 (/lib/modules/2.6.12-9-k7/kernel/drivers/cdrom/cm206.ko): Input/output error
Apr  7 23:46:04 localhost kernel: [4898616.448000] kjournald starting.  Commit interval 5 seconds
Apr  7 23:46:05 localhost kernel: [4898616.455000] EXT3 FS on sdc2, internal journal
Apr  7 23:46:05 localhost kernel: [4898616.455000] EXT3-fs: recovery complete.
Apr  7 23:46:05 localhost kernel: [4898616.455000] EXT3-fs: mounted filesystem with ordered data mode.

Thanks again.

d0odman · 04-08-2006, 02:03 AM

Check out what the attributes are for the sdc entries in /dev/.static and I'm sure you'll find that the major number is 32, not 8 as you had it. That cm206.ko error would come up if you don't have that hardware on your system. If you don't, then that module is being loaded up somewhere you don't know about. That other error about the type thing is a new one for me, so I don't really have an explanation for it.

demoman · 04-08-2006, 02:11 PM

Quote:

Originally Posted by d0odman

Check out what the attributes are for the sdc entries in /dev/.static and I'm sure you'll find that the major number is 32, not 8 as you had it.

Actually it seems to be 8 - but I have to admit I am not too sure what this means (failed to google any simple explanation of this).

Code:

# ls -l /dev/.static/dev/sdc*
brw-rw----  1 root disk 8, 32 2005-09-26 02:11 /dev/.static/dev/sdc
brw-rw----  1 root disk 8, 33 2005-09-26 02:11 /dev/.static/dev/sdc1

In any case, many thanks again for the directions as I now have a workaround!

d0odman · 04-08-2006, 02:22 PM

A ha, yes, OK, I read the devices.txt file wrong. sdc is block major 8, while 32 references the whole disk. 33, 34, etc refer to the partitions, starting numbering from 1, with a limit of 15. If you're bored, you can check out that file included with the kernel source, in linux/Documentation. To add the devices in to /dev, mknod as above, but with "b 8 32", "b 8 33", etc, all the way to sdc15. If you use udev, those devices get automagically created, or they should be, or removed, depending on if they exist or not. Sorry for the blunder.

JZL240I-U · 04-13-2006, 05:03 AM

In case you don't know these, they might help a little:

http://www.reactivated.net/writing_udev_rules.html
http://ftp.kernel.org/pub/linux/util...tplug/udev-FAQ

demoman · 04-14-2006, 12:08 AM

Quote:

Originally Posted by JZL240I-U

In case you don't know these, they might help a little:

http://www.reactivated.net/writing_udev_rules.html
http://ftp.kernel.org/pub/linux/util...tplug/udev-FAQ

That's great info. I didn't know much about udev. I'll play with this over the WE.
Thanks!