Here is absolutely minimal application so you could try to reproduce it on your machine. Having two files for example in /home/aln/tmp/tw_test: server.tac MyLib.py MyLib.py class Solver(object): def solve(self): """ do extremely complex stuff here """ print "Hello from solve" server.tac #!/usr/bin/python import MyLib from twisted.application import internet, service from twisted.internet import protocol, reactor, defer, utils, threads from twisted.protocols import basic class MyProtocol(basic.LineReceiver): def lineReceived(self, line): if line=="new job": self.transport.write("started a job" + '\r\n') self.factory.run_defered() class MyFactory(protocol.ServerFactory, MyLib.Solver): protocol = MyProtocol def run_defered_helper(self): self.solve() def run_defered(self): d = threads.deferToThread(self.run_defered_helper) application = service.Application('MyApplication') factory = MyFactory() internet.TCPServer(1079, factory).setServiceParent(service.IServiceCollection(application)) Everything works fine when I start it under non-root user. aln@aln-laptop:tw_test$ twistd -ny server.tac 2010-03-03 22:42:55+0300 [-] Log opened. 2010-03-03 22:42:55+0300 [-] twistd 8.2.0 (/usr/bin/python 2.6.4) starting up. 2010-03-03 22:42:55+0300 [-] reactor class: twisted.internet.selectreactor.SelectReactor. 2010-03-03 22:42:55+0300 [-] <class 'MyFactory'> starting on 1079 2010-03-03 22:42:55+0300 [-] Starting factory <MyFactory object at 0x2d5ea50> 2010-03-03 22:42:59+0300 [MyProtocol,0,127.0.0.1] Hello from solve ^C2010-03-03 22:43:01+0300 [-] Received SIGINT, shutting down. 2010-03-03 22:43:01+0300 [-] (Port 1079 Closed) 2010-03-03 22:43:01+0300 [-] Stopping factory <MyFactory object at 0x2d5ea50> 2010-03-03 22:43:01+0300 [-] Main loop terminated. 2010-03-03 22:43:02+0300 [-] Server Shut Down. But if try to start it under root (which is going to happen in my real application) I receive the following exception: aln@aln-laptop:tw_test$ sudo twistd -ny server.tac [sudo] password for aln: Traceback (most recent call last): File "/usr/lib/python2.6/dist-packages/twisted/application/app.py", line 694, in run runApp(config) File "/usr/lib/python2.6/dist-packages/twisted/scripts/twistd.py", line 23, in runApp _SomeApplicationRunner(config).run() File "/usr/lib/python2.6/dist-packages/twisted/application/app.py", line 411, in run self.application = self.createOrGetApplication() File "/usr/lib/python2.6/dist-packages/twisted/application/app.py", line 494, in createOrGetApplication application = getApplication(self.config, passphrase) --- <exception caught here> --- File "/usr/lib/python2.6/dist-packages/twisted/application/app.py", line 505, in getApplication application = service.loadApplication(filename, style, passphrase) File "/usr/lib/python2.6/dist-packages/twisted/application/service.py", line 390, in loadApplication application = sob.loadValueFromFile(filename, 'application', passphrase) File "/usr/lib/python2.6/dist-packages/twisted/persisted/sob.py", line 215, in loadValueFromFile exec fileObj in d, d File "server.tac", line 2, in <module> import MyLib exceptions.ImportError: No module named MyLib Failed to load application: No module named MyLib If I try to load MyLib module in the python intepreter under root, it works fine: aln@aln-laptop:tw_test$ sudo python Python 2.6.4 (r264:75706, Dec 7 2009, 18:43:55) [GCC 4.4.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import MyLib >>> import sys >>> print(sys.path) ['', '/usr/lib/python2.6', '/usr/lib/python2.6/plat-linux2', '/usr/lib/python2.6/lib-tk', '/usr/lib/python2.6/lib-old', '/usr/lib/python2.6/lib-dynload', '/usr/lib/python2.6/dist-packages', '/usr/lib/python2.6/dist-packages/PIL', '/usr/lib/python2.6/dist-packages/gst-0.10', '/usr/lib/pymodules/python2.6', '/usr/lib/python2.6/dist-packages/gtk-2.0', '/usr/lib/pymodules/python2.6/gtk-2.0', '/usr/local/lib/python2.6/dist-packages'] >>> sys.path is absolutely the same for aln user. I tried sudo -E too. Any suggestions?