Linux

Would this work

Yes.

or would I have problems

Also yes.

I used to do this backing up my "servers". By that I mean some Raspberry Pis and random old PCs running Debian. I even did so successfully when needing to restore the images. But it was fragile and also failed at times, sometimes to great inconvenience when it was a machine serving something important.

I've since moved to a different backup strategy for servers, but if I were to do this with a bare-metal machine I want to preserve, I'd use something like Clonezilla. The maintainers of that project know a whole heck of a lot more than I do of the ins and outs of disk management, backup, and restoration than I do with my simple dd commands. If it is something you're just wanting to do for fun and experience, dd can work. If you're concerned with the security of your data/image, I'd use Clonezilla.

As long as it's not a mounted and running live system, it should work. Not the most efficient way to do such a thing, but I would think it should work.

Don't do this. If you have a 1TB drive with only 10GB being occupied, your image will be 1TB, and you will need a >1TB drive to store it, and another to restore it.

If you only backup the data you could do it in a much smaller size drive and it will be a lot faster to perform backups (otherwise you will need hours every time you want to create a new image).

Works fine, though it's not an "iso" file. But it doesn't matter what extension you use.

I used to do this to switch an old laptop between Windows and Linux. I'd backup one, overwrite with the other. Swap as necessary.

Should work. You'd be better off dd'ing each partition separately.

Yes. Make sure neither are mounted.

Use larger block sizes with bs=<like, idk, 16M> will make it go faster.

Many years ago I tried it, but didn't really read up on it. Wanted to back up my Pi's sdcard while the system was running. I even fucking named that script "online-backup".

Now every time I ran that, after hours, I noticed my Pi was crashing, and never booted back up. I used chinese sd cards so I blamed it on them.

But this happened multiple times, just to learn I was using dd absolutely wrong.

dd was always a scary utility to me, and still is. I fucked up things with dd, regardless I quadruple checked everything 😅

but to answer the question; it's possible, but you really need to know what are you doing.

Check out Clonezilla, which is the perfect tool for the job.

I have done this a few times, so long as the drive isn't mounted it works fine.

One advantage of this approach compared to clonezilla is you can pipe it through netcat or similar and move it to another machine. You can also first pipe it through gzip as well to save on the transfer bytes a bit as well and then on the other end just store the compressed image or unzip it. Combine a few tools together and you have quite a lot of capability for complete image backups but its usually best done for the boot drives from a live USB.

This will definitely work. I did this recently when upgrading a Steam Deck to a bigger drive. Other suggestions below are probably faster though.

you can even mount the image as a loop device (i suggest read only (ro)) to extract files

Like everyone has said there’s way better ways of doing it.

HOWEVER if you wanted to use dd you totally could. I’d recommend piping into something like gzip/zstd to save some space though.

dd if=/dev/sda | gzip >/mnt/backup_disk/sda.gz

You could also use restic backup the raw block device too.

That being said, clonezilla is exactly what you want

It would technically work, yes.

But also, you're wasting a lot of storage space that way, especially if you do it often. You really only should backup your home directory, it contains all your data. You can simply re-install the rest from the internet.