Watchdog: watchmedo auto-restart broken on OS X due to its setsid usage (OSError: [Errno 2] No such file or directory)

Created on 19 Jul 2015 · 7Comments · Source: gorakhargosh/watchdog

https://github.com/gorakhargosh/watchdog/pull/225/files added a setsid call when running a command via auto-restart. This command is not available on OS X leading to:

$ watchmedo auto-restart -- MY-COMMAND-HERE
Traceback (most recent call last):
  File "/Users/nickolay/temp-env/bin/watchmedo", line 9, in <module>
    load_entry_point('watchdog==0.8.3', 'console_scripts', 'watchmedo')()
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/watchdog/watchmedo.py", line 566, in main
    parser.dispatch()
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/argh/helpers.py", line 55, in dispatch
    return dispatch(self, *args, **kwargs)
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/argh/dispatching.py", line 174, in dispatch
    for line in lines:
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/argh/dispatching.py", line 277, in _execute_command
    for line in result:
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/argh/dispatching.py", line 231, in _call
    result = function(namespace_obj)
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/watchdog/watchmedo.py", line 541, in auto_restart
    handler.start()
  File "/Users/nickolay/temp-env/lib/python2.7/site-packages/watchdog/tricks/__init__.py", line 147, in start
    self.process = subprocess.Popen(self.command)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 1335, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

Judging from https://docs.python.org/3/library/subprocess.html

If you need to modify the environment for the child use the env parameter rather than doing it in a preexec_fn. The start_new_session parameter can take the place of a previously common use of preexec_fn to call os.setsid() in the child.

...this might be doable in pure python (at least on Unix). Since watchdog supports Python 2.6, it probably would have to use preexec_fn instead of start_new_session.

Source

nickolay

Most helpful comment

So I just found my own response on #329 from almost a month ago when looking into this issue for a colleague, so I'd figure I'd mention what I did to fix it, for the next time I happen upon this page...

pip install git+https://github.com/gorakhargosh/watchdog.git

TotempaaltJ on 2 Mar 2017

👍12

All 7 comments

Changing https://github.com/gorakhargosh/watchdog/blob/master/src/watchdog/tricks/__init__.py#L125 in the following two places works for me on OS X 10.9.5:

< 141        self.command = ['setsid'] + command
> 141        self.command = command

  146     def start(self):
< 147         self.process = subprocess.Popen(self.command, preexec_fn=os.setsid)
> 147         self.process = subprocess.Popen(self.command)

I didn't test with the original case from PR 225 and this might work incorrectly on Windows (os.setsid seems unsupported there, and I'm not sure how os.killpg works there).

nickolay on 19 Jul 2015

This is already addressed by #329.