twistd plugin permissions problem causes users to think that tahoe-lafs unit tests failed

[nejucomo]

I just installed 1.6.1 on an osx 10.6 box, seemingly successfully: $ python ./setup.py build ... Output attached.

But when I run unittests many fail: $ python ./setup.py test ... Output attached.

The first failure appears before unittest output, and may be irrelevant:

Traceback (most recent call last):
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/python/usage.py", line 241, in parseOptions
    self.postOptions()
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/scripts/trial.py", line 293, in postOptions
    self['reporter'] = self._loadReporterByName(self['reporter'])
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/scripts/trial.py", line 279, in _loadReporterByName
    for p in plugin.getPlugins(itrial.IReporter):
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/plugin.py", line 200, in getPlugins
    allDropins = getCache(package)
--- <exception caught here> ---
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/plugin.py", line 179, in getCache
    dropinPath.setContent(pickle.dumps(dropinDotCache))
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/python/filepath.py", line 623, in setContent
    f = sib.open('w')
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/python/filepath.py", line 433, in open
    return open(self.path, mode+'b')
exceptions.IOError: [Errno 13] Permission denied: '/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/twisted/plugins/dropin.cache.new'

[nejucomo]

The installation output on osx 10.6

[nejucomo]

The output of: $ python ./setup.py test

[nejucomo]

From irc:

ducki2p 11:20 
thats a known twisted issue; you need to run twistd --help as root once to complete its setup
nejucomo 11:24 
Oh, thanks!
24:45
I wonder if we need to modify the install instructions for tahoe-lafs in that case.

I did indeed run "sudo twistd --help" then reran the unittests and this exception went away. Attached the new unittest logs.

Notice however there are still failures documented in ticket #1006.

[nejucomo]

The unittests after running "sudo twistd --help".

[zooko]

This is ​Twisted #2409 but let's leave this ticket (Tahoe-LAFS #1005) open in case we can figure out a work-around, possibly involving invoking sudo twistd --help at some point or at least updating the documentation to ask the user to do so.

[davidsarah]

The ​fix for ​Twisted #2409 was released in Twisted v11.0. I don't think we need to do anything to work around it in Tahoe-LAFS; the problem will go away as people use newer versions of Twisted.

[davidsarah]

Note that fixed versions of Twisted will still print the single line "Unexpected error while writing cache file". We might want to document that that is harmless.