Please try deja-dup-37.0-1.fc26 from updates-testing.

I tried and obtained the same error

Can you run it with gdb and provide a backtrace?

Created attachment 1359892 [details]
Stacktrace

gdb stacktrace

Backtrace attached... not sure it is exactly what you need, btw, if it's not sorry, and please let me know how to get the correct backtrace

It's a good start. What storage type are you using?

(In reply to Gwyn Ciesla from comment #6)
> It's a good start. What storage type are you using?

An ext4 SATA 2GB HD (whose filesystem is mounted as / and deja-dup is installed there), but let me point out that I am trying to start deja-dup without connecting my external USB hard drive. Maybe you mean "storage where deja-dup would save files to"? In that case, that storage is disconnected now, because I wanted to narrow down the problem. Does it make sense?

Yes, the backup destination, sorry for being unclear. :)

E_COFFEE

Does it crash the same way whether the drive is connected or not?

(In reply to Gwyn Ciesla from comment #8)
> Yes, the backup destination, sorry for being unclear. :)
> 
> E_COFFEE
> 
> Does it crash the same way whether the drive is connected or not?

Appartently YES, but don't now it for sure... do you need a backtrace in this situation, too?

To be precise, the problem is a bit more complicated because it happens something slightly different:

- If I connect the USB Hard Disk:
  - the scheduled backup starts and fails (saying "Another duplicity instance is already running with this archive directory" in the deja-dup Gnome window)
    - if I leave the window open, running deja-dup from terminal outputs "GDBus.Error:org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message bus without replying";
   - else, if I close the window and run deja-dup from terminal, it outputs the segfault only.

Do you have any duplicate RPMs on your system after the upgrade?

Sorry, I cannot find a certain way to search for them... can I have a hint please? Thanks

sudo dnf repoquery --duplicates

If there are some, 

sudo dnf remove --duplicates

Also, check 

sudo dnf repoquery --unsatisfied

both the commands

sudo dnf repoquery --duplicates

and

sudo dnf repoquery --unsatisfied

output is empty.

And you have duplicity 0.7.15-1?

(In reply to Gwyn Ciesla from comment #14)
> And you have duplicity 0.7.15-1?

yes, exactly

Do backups work on a different storage destination, like ssh, smb, etc?

Yeah, I would like to give some tries, but the problem is that in no way I am able to run the program :-/ ... or, am I missing something?

Try changing the settings, you can do so with gsettings. See what's available with:

gsettings list-recursively org.gnome.DejaDup

I have done some tries:
- deleted all old backup files from my backup drive, to be sure the problem is not related to them
- changed the "include list" in dconf, and set it to "['/tmp']" (quotes for clarity only), to be sure the problem is not related to it

--> the backup starts when I connect the USB drive, completes correctly, but if I run deja-dup from terminal I get segfault again. So, the only way I know to run the backup here is by connecting the drive (also by tweaking the last-backup time, setting it to the past, to trigger it immediately)

- changed backend from "drive" to "local" in dconf

--> again, running deja-dup (from terminal or by the gnome menu) does not work, so I run it by setting the last-backup parameter in dconf. The backup starts and completes correctly.

- also tried to backup to a smb share --> same behaviour

So, it seems to me that the segfault is not related to anything pointed out above.

Ok, I'm out of ideas. I filed an upstream bug.

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Now working with deja-dup 37.1, duplicity 0.7.17 in F27