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Re: USB drive mounted Read-only; what to do ?



Brian wrote:
> Bob Proulx wrote:
> > floppy group.  The console user is also set up with the floppy group
> > too.  Assuming one of libpam, consolekit, systemd-login0 and so forth.
> > Therefore the console user doesn't need to be root.  They can write to
> > the write to it directly.
> 
> It is assumed you are doing this on Wheezy. You are then the 100% correct.

Hopefully Stable is a good default assumption unless there is some
reason to assume otherwise.

> For me:
> ...
>   brw-rw---T 1 root floppy 8, 16 Dec 20 23:04 /dev/sdb
> /dev/sdb is a USB stick I've just plugged in. I am a member of the
> floppy group because d-i set the machine up that way many years ago.

Ah, yes, even without libpam, consolekit, systemd-login0 it is *also*
possible that the user is in the floppy group by specification in the
/etc/group file too.  Another "and so forth" possibility.

> Being a member of the floppy group on testing or unstable doesn't confer
> the same privileges as it does on Wheezy.

Hmm...

> From the udev changelog of Sat, 26 Apr 2014 21:37:29 +0200.
> 
>   * Drop our Debian specific 50-udev-default.rules and 91-permissions.rules
>     and use the upstream rules with a patch for the remaining Debian specific
>     default device permissions. Many thanks to Marco d'Itri for researching
>     which Debian-specific rules are obsolete! Amongst other things, this now
>     also reads the hwdb info for USB devices (Closes: #717405) and gets rid of
>     some syntax errors (Closes: #706221)
> 
> 91-permissions.rules is the one to look at.

Good pointer.  Thanks for bringing this to my attention.

Sure enough on my Sid system usb storage devices are no longer placed
into the floppy group.  I hadn't notice this yet.  Below I have just
inserted a USB storage on a Sid system.

  $ ll /dev/sdg*
  brw-rw---- 1 root disk 8, 96 Dec 20 17:25 /dev/sdg
  brw-rw---- 1 root disk 8, 97 Dec 20 17:25 /dev/sdg1
  brw-rw---- 1 root disk 8, 98 Dec 20 17:25 /dev/sdg2

Set up as disk and not floppy.  Good heads up that things have
changed.  Hmm...  Seems like a change for the worse.

> How does a user now get to use fdisk or write to a USB stick without libpam
> etc and "so forth"? Or does it matter?

Good question.  It feels like we have come full circle.  That was the
way it was before the introduction of devfs and udev.  It appears that
things now have returned to the way it was before udev.  Which won't
bother the old-school Unix folks because we already lived through that
and already know how to deal with it.  But why haven't the next
generation started complaining about it?  If it works for them, then
how?  The changelog says they are obsolete.  But then what is the
replacement for them?

Bob

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