[vox-tech] how to access the content in the usb flash

[Donald Greg McGahan]

Just a follow on to this, because I am relatively new to *nix myself. A
friend suggested I try tail -f /var/log/messages at a command line in a
terminal as root, prior to plugging in the USB device. I then see the
information about the device when I plug it in. For me this is much
simpler than slogging through dmesg. 

I also send thanks because I've never used pmount and will give it a
try. I started with Debian then Ubuntu, but now find that I like
Xubuntus XFCE desktop. Anyway, it uses ivman so that using the
graphical file manager thunar it shows the device when plugged in. 

DiG McGahan

--- Hai Yi <yihai2004 at gmail.com> wrote:

> Thanks to both Pete and Ken!
> Ken, I appreciate your long and detailed explaination, which is very
> helpful and I made it by following the instructions. of cause there
> is
> a lot for me to digest yet. :)
> 
> Hai
> 
> 
> On 7/12/06, Ken Bloom <kbloom at gmail.com> wrote:
> > On Tuesday 11 July 2006 22:16, Hai Yi wrote:
> > > Hello there:
> > >
> > > I have a creative flash with a usb port, after I plugged it in
> the
> > > port, I see this:
> > >
> > > $ lsusb
> > >
> > > Bus 003 Device 004: ID 041e:4139 Creative Technology, Ltd
> > > Bus 003 Device 001: ID 0000:0000
> > > Bus 002 Device 001: ID 0000:0000
> > > Bus 001 Device 004: ID 06cb:0003 Synaptics, Inc.
> > > Bus 001 Device 003: ID 045e:0053 Microsoft Corp.
> > > Bus 001 Device 001: ID 0000:0000
> > >
> > > Then I issued a command (might be wrong)
> > > mount -t usbfs /proc/bus/usb/003/004 /mnt/
> > >
> > > Then I am struck in the middle of nowhere, don't know how to
> proceed
> > > to access the content in my flash.
> >
> > # umount /mnt
> >
> > While what you tried seems like a very logical command, it's really
> the
> > completely wrong tack, for several reasons:
> >
> > a) lsusb doesn't give you the information you need to mount the
> drive
> > b) /proc/bus/usb/003/004  isn't a device node
> > c) usbfs isn't a way of accessing data on a USB device.
> >
> > A device node is a special kind of file living somewhere in /dev
> that
> > when read from or written to, passes through the device driver and
> > actually talks to the device.
> >
> > The information you're looking for when you mount a device is
> actually
> > printed by the kernel when you attach the device. If you're using X
> > window, then you won't see it, but no worries. You can always see
> the
> > log of kernel messages by typing dmesg (as a normal user). Here's
> the
> > relevant portion of my dmesg when I attach my thumb drive:
> >
> > usb 1-1: new full speed USB device using uhci_hcd and address 2
> > usb 1-1: configuration #1 chosen from 1 choice
> > SCSI subsystem initialized
> > Initializing USB Mass Storage driver...
> > scsi0 : SCSI emulation for USB Mass Storage devices
> > usbcore: registered new driver usb-storage
> > USB Mass Storage support registered.
> > usb-storage: device found at 2
> > usb-storage: waiting for device to settle before scanning
> >   Vendor: SanDisk   Model: U3 Cruzer Micro   Rev: 2.15
> >   Type:   Direct-Access                      ANSI SCSI revision: 02
> >   Vendor: SanDisk   Model: U3 Cruzer Micro   Rev: 2.15
> >   Type:   CD-ROM                             ANSI SCSI revision: 02
> > usb-storage: device scan complete
> > SCSI device sda: 990865 512-byte hdwr sectors (507 MB)
> > sda: Write Protect is off
> > sda: Mode Sense: 03 00 00 00
> > sda: assuming drive cache: write through
> > SCSI device sda: 990865 512-byte hdwr sectors (507 MB)
> > sda: Write Protect is off
> > sda: Mode Sense: 03 00 00 00
> > sda: assuming drive cache: write through
> >  sda: sda1
> > sd 0:0:0:0: Attached scsi removable disk sda
> >
> > The relevant line is the following:
> >  sda: sda1
> > this line is the list of device files corresponding to the
> partitions on
> > the thumb drive. (Yes, you can have multiple partitions)
> >  * sda is the device file corresponding to the whole drive.
> >  * the drive has one partition, named sda1.
> > You want to mount sda1. The device files are found in /dev, so you
> want
> > to issue some variant of the command "mount /dev/sda1 /mnt"
> >
> > usbfs is completely the wrong filesystem type. It's simply an
> > informational filesystem[1], kinda like proc (mounted on /proc) or
> > sysfs (mounted on /sys) that doesn't contain any real data on any
> disk.
> > It also doesn't take a device name. Actually, it takes a path to a
> > device and completely ignores it, not even bothering to check that
> it
> > exists, so by convention something like "none" or "usbfs" is used.
> > However, when you told it that /proc/bus/usb/003/004 was the device
> > file, that was allowed too. It completely ignored it and mounted
> the
> > informational filesystem on /mnt (and didn't spew out any error
> > messages because you hadn't actually done anything wrong from the
> > system's point of view).
> >
> > The filesystem on your flash drive (unless you reformatted it) is
> of
> > type vfat. So the correct, fully specified command would be "mount
> -t
> > vfat /dev/sda1 /mnt". It's not actually necessary to specify the
> > filesystem type though -- the kernel can autodetect the file system
> > type, so the command I gave before ("mount /dev/sda1 /mnt") would
> also
> > work just fine.
> >
> > But there's a better way to mount this...
> >
> > You have to run the mount command as root (which I'm sure you did)
> to
> > mount a usb device. This is becuase when USB devices came along,
> they
> > completely broke the kernel's old way for users to mount their own
> > disks. Back in the days of floppies, a device always had the same
> > device nodes. When you inserted a floppy disk, you *knew* that it's
> > device node was /dev/fd0. USB changed all that. Since you could now
> > plugin as many USB devices as you wanted, in as many orders as you
> > wanted, and they all showed up as SCSI disks (/dev/sd*), they began
> to
> > move around. The old method of specifying a device that users could
> > mount in /etc/fstab broke, because now there were many devices.
> >
> > So the distributions created pmount. A user in the plugdev group
> can
> > mount a USB device to a mountpoint in /media in a very simple
> > way: "pmount /dev/sda1" (replacing, of course the device name with
> the
> > one you discovered above using dmesg). The mountpoint on which this
> is
> > mounted is /media/sda1. When you're ready to unmount the device,
> you
> > use the command "pumount sda1". Now you don't need to be root.
> >
> > But IMO, this system still sucks because you still need to discover
> the
> > right device file on your own[2]. udev has some techniques to
> always
> > guarantee the same device name, but that doesn't work in general
> > because it only works for USB keys that the system administrator
> > configures the system to know about in advance. If you went to a
> public
> > computer lab and tried, you'd be SOL.
> >
> > Looking around, I see a Debian package which may help:
> > [bloom at cat-in-the-hat ~]$ apt-cache show usbmount
> > Package: usbmount
> > Priority: extra
> > Section: admin
> > Installed-Size: 116
> > Maintainer: Martin Dickopp <martin at zero-based.org>
> > Architecture: all
> > Version: 0.0.14-0.1
> > Depends: udev (>= 0.084-2), lockfile-progs
> > Filename: pool/main/u/usbmount/usbmount_0.0.14-0.1_all.deb
> > Size: 10494
> > MD5sum: 1b74998193fe32a6e05eca5232e605db
> > SHA1: d52ca0d42689842f6b9e977d8c4ef02f1cbbff53
> > SHA256:
> 950c4dd2ca67dc8daefff22242db2cecf2aac87169cd9259f64c8648fa11b3c9
> > Description: automatically mount and unmount USB mass storage
> devices
> >  This package automatically mounts USB mass storage devices
> (typically
> >  USB pens) when they are plugged in, and unmounts them when they
> are
> >  removed. The mountpoints (/media/usb[0-7] by default), filesystem
> types
> >  to consider, and mount options are configurable. When multiple
> devices
> >  are plugged in, the first available mountpoint is automatically
> >  selected. If the device provides a model name, a symbolic link
> >  /var/run/usbmount/MODELNAME pointing to the mountpoint is
> automatically
> >  created.
> >  .
> >  The script that does the (un)mounting is called by the udev
> daemon.
> >  Therefore, USBmount requires a 2.6 (or newer) kernel.
> >  .
> >  USBmount is intended as a lightweight solution which is
> independent of
> >  a desktop environment. Users which would like an icon to appear
> when an
> >  USB device is plugged in should use the pmount and hal packages
> >  instead.
> >  .
> >  Homepage: http://usbmount.alioth.debian.org/
> > Tag: admin::configuring, admin::filesystem, hardware::storage,
> 
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