Comment 27 for bug 234835

>Ok so, this problem seems to be caused by running ubiquity within a
>liveboot that was booted from an iso file on the hdd (in my case I used
>grub2's loopback interface). It would seem that the migration assistant
>wanted to access other files on the partition that had the iso on it and
>refused to run without unmounting the partition, which I assumed
>wouldn't be good for the live system.

>Simply calling ubiquity using "ubiquity --no-migration-assistant" from
>the command line instead of the shortcut on the live desktop prevented
>the migration assistant from complaining.

>It would be nice if ubiquity could tell that the liveboot came from an
>iso file that is still mounted, (ie check if the /isodevice (created I
>assume by grub2) mount folder exists and offer to not run the migration
>assistant, either at all or give a warning and then use the assistant on
>the other partitions that it can access.

> ALL IN ALL THIS ISN'T REALLY A BUG!

I disagree. the fact that you can explain exactly how "properly behaving" programs end up doing something unexpected when combined, does not mean that it isn't a bug.

In this case, "it crashes" is definitively unwanted behavior, and whatever-it-takes should be done to prevent the end user getting confronted with this situation. (several decades ago, there was this daemon that would send "you have mail" messages to the logged in users. The mailer was supposed to send it the tty where the user was logged in, and the subject of the Email. unprivileged users could link /etc/passwd to /tmp/a and then send it: tty: ../tmp/a (8 chars max) and subject: bla\nmyroot::0:0::/:/bin/sh which worked exactly as specified in the manual....)