Re: Some help with dd backing up into an iso

[David Wright <deblis@lionunicorn.co.uk>]

On Tue 07 Mar 2017 at 20:25:30 (+0100), Thomas Schmitt wrote:
> Hi,
> 
> i wrote:
> > > It has its use cases. E.g. before you put a Debian installation ISO
> > > onto an USB stick, it can be used to backup the old stick content
> 
> David Wright wrote:
> > Why would you now copy the old stick content onto the stick again?
> 
> When you no longer need the installation ISO because the installation
> is done, wouldn't it be nice to get the DOS formatted USB stick back
> for carrying files between computers ?

Forgive me for asking, but have you read the OP?

The OP said they had a USB stick containing 1.7GB of data on it.
They copied the stick to a file, usbfilename.iso, with dd.
They then copied usbfilename.iso back onto the stick in order to
"test the validity" by running dd with if=/of= reversed.

There was no indication whether the stick contained a bunch of jessie
.deb files or a copy of their doctoral thesis. Either way, I can't see
the sense of backing up a filesystem to an image file and then, for
the sake of it, using the image file to overwrite the original filesystem.

And, assuming the process was left to completion (which it wasn't),
what validity would have been tested? What would constitute a pass,
and what would distinguish a fail?

There was no indication that the stick had been used for something
else in the interim.

> A plain dd copy of the stick provides boot sector, partitioning,
> filesystem, and data file content in one sweep. No fdisk, no mkfs,
> no grub-install, no restoring of a backup archive needed.

Yes, yes, this is back to the technical details of making copies.
That wasn't the subject of my first post and I said as much.

> > That's what the OP wrote that they did, in order to "test the validity".
> 
> Since she or he knows punching cards, i assume that there is knowledge
> of Murphy's Law, too.
> 
> > ¹We had two glitches yesterday evening as the tornadoes went by.
> 
> I have a UPS between power provider and computer. Murphy's law ...

…which cost €...?

Cheers,
David.