USB Detection; when /dev/sda1 or /dev/sdb1

ravime · 09-10-2007, 10:18 AM

Dear all,

As I know USB will deteceted as eaither /dev/sda1 or /dev/sdb1.

I would like to know when USB will be detected as /dev/sda1 or /dev/sdb1.
on which it sda1 and sdb1 depends.

Thanks for any input.

rufius · 09-10-2007, 10:30 AM

Well its up to the udev system to decide. If it believes that /dev/sda exists currently in the system (even if its not really there), its going to mount as /dev/sdb. There's no sure-fire way to ensure that it'll always be one or the other unless are thorough in your proper umounting/mounting. Even then, its not guaranteed. What is your end goal?

jschiwal · 09-10-2007, 11:33 AM

If you want to write an fstab entry for a usb external storage device, use "UUID=<the_uuid_number>" or "LABEL=<label>" instead. I have a thumbdrive where I used "mlabel" to label the drive as "PODCASTS". An fstab entry for it could use "LABEL=PODCASTS" instead of the device node.

Even without an fstab entry, udev notices the label and it is mounted at /media/PODCASTS.

ravime · 09-11-2007, 08:43 AM

Quote:

Originally Posted by rufius

Well its up to the udev system to decide. If it believes that /dev/sda exists currently in the system (even if its not really there), its going to mount as /dev/sdb. There's no sure-fire way to ensure that it'll always be one or the other unless are thorough in your proper umounting/mounting. Even then, its not guaranteed. What is your end goal?

Basically I am running Desktop with LIVE-CD, Whenever system boots up I would like to copy few files from USB to Livecd environment, then operate.
So whenever system boots up I am mounting the USB as /deev/sda1. Sometimes mount fails because USB is detected as /dev/sdb1, resulting failure in next execution also. So I want to make sure on what basis it OS decides it as /dev/sda1 or /dev/sdb1

Regards
ravime

ravime · 09-11-2007, 08:45 AM

Quote:

Originally Posted by jschiwal

If you want to write an fstab entry for a usb external storage device, use "UUID=<the_uuid_number>" or "LABEL=<label>" instead. I have a thumbdrive where I used "mlabel" to label the drive as "PODCASTS". An fstab entry for it could use "LABEL=PODCASTS" instead of the device node.

Even without an fstab entry, udev notices the label and it is mounted at /media/PODCASTS.

thanks for your kind reply.

I am operating in LIVECD environment. so there is no fstsb entry.

jschiwal · 09-11-2007, 08:46 AM

Does your live cd use udev & hal? Look in /dev/ for directories like /disk-by-label/ & /disk-by-uuid and use those device links in your mount command.

ravime · 09-12-2007, 06:15 AM

Quote:

Originally Posted by jschiwal

Does your live cd use udev & hal? Look in /dev/ for directories like /disk-by-label/ & /disk-by-uuid and use those device links in your mount command.

Thank you very much. I was trying for shortcut. But no shortcut, I feel.
I should check /dev directory as you said.