/usr/bin/add-apt-repository:OSError:/usr/bin/add-apt-repository@163:add_source_from_shortcut:set_modified_sourceslist:save_sourceslist:backup:copy:copyfile

Traceback:

Traceback (most recent call last):
  File "/usr/bin/apt-add-repository", line 163, in <module>
    if not sp.add_source_from_shortcut(shortcut, options.enable_source):
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 750, in add_source_from_shortcut
    self.set_modified_sourceslist()
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 484, in set_modified_sourceslist
    self.save_sourceslist()
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 649, in save_sourceslist
    self.sourceslist.backup(".save")
  File "/usr/lib/python3/dist-packages/aptsources/sourceslist.py", line 383, in backup
    shutil.copy(source.file, "%s%s" % (source.file, backup_ext))
  File "/usr/lib/python3.4/shutil.py", line 228, in copy
    copyfile(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.4/shutil.py", line 108, in copyfile
    with open(dst, 'wb') as fdst:
OSError: [Errno 30] Read-only file system: '/etc/apt/sources.list.save'

This is because it is being run on a device where the partition containing /etc/apt is read-only.

Status changed to 'Confirmed' because the bug affects multiple users.

@ Brian Murray

If you think this bug is caused by an user misconfiguration, please set its status to "invalid".

Ubuntu devices are setup with a read-only root file system so this is a supported use case and software-properties should not crash in this situation. I seem to recall it being fixed but couldn't find anything in the software-properties changelog supporting that.