click packages fail with mysterious error when disk is full

[Brendan Donegan]

Sometimes I get the following error when trying to manually install a click package. Package works fine in other systems
                              pkcon install-local com.canonical.scopes.etsy_1.0.10_armhf.click mhf.click
Installing files [=========================]
Finished [=========================]
Installing files [=========================]
Waiting for authentication [=========================]
Starting [=========================]
Finished [=========================]
Fatal error: /home/phablet/clicks/com.canonical.scopes.etsy_1.0.10_armhf.click failed to install.
Traceback (most recent call last):
  File "/usr/bin/click", line 86, in <module>
    sys.exit(main())
  File "/usr/bin/click", line 82, in main
    return mod.run(args)
  File "/usr/lib/python3/dist-packages/click/commands/install.py", line 57, in run
    package_path, user=options.user, all_users=options.all_users)
  File "/usr/lib/python3/dist-packages/click/install.py", line 384, in install
    path, user=user, all_users=all_users)
  File "/usr/lib/python3/dist-packages/click/install.py", line 344, in _unpack
    env=env, **kwargs)
  File "/usr/lib/python3.4/subprocess.py", line 556, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python3.4/subprocess.py", line 537, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.4/subprocess.py", line 858, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1457, in _execute_child
    raise child_exception_type(err_msg)
subprocess.SubprocessError: Exception occurred in preexec_fn.

This appears to be because the disk is full. As well as making this error cleaner and clearer, some general testing should be done around what happens when we try to install click apps when the disk is full.

[Launchpad Janitor (janitor)]

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

[Michael Vogt (mvo)]

We can do multiple things here, we can test before install via statvfs() if there is enough free space, but that won't help if the spacing is filling up while installing. So we need to ensure dpkg reports a out-of-diskspace error via e.g. the status-fd (which we are currently not using AFAIK.