Hi! I have written about this to Haskell cafe and they advised me to write it here. I have a problem that I cannot open /dev/rfcomm0 device if I compile my program with -threaded option. Like: fd <- openFd "/dev/rfcomm0" ReadWrite Nothing OpenFileFlags { append = False, noctty = True, exclusive = False, nonBlock = True, trunc = False } If I compile my program with -threaded option I always get such error: interrupted (Interrupted system call) But without -threaded it works flawlessly. I am using Linux 2.6.30 amd64, GHC 6.10.4. It was the same with 6.8. And I have tested it also on 6.12.1. After some testing I have discovered that the problem is only with /dev/rfcomm0 as a device, that is with Bluetooth serial connection. The problem is that rfcomm Linux kernel code contains: if (signal_pending(current)) { err = -EINTR; break; } So if during open call some signal comes it returns EINTR. As it has to open a connection to a Bluetooth device opening a /dev/rfcomm0 file requires some time and during that time obviously there is some signal sent by GHC with -threaded option which is not sent without it. So please tell me what is the difference between open with and without -threaded option in GHC as I would like to make a simple C test case. I am not really sure if this is a feature or a bug in Linux Bluetooth kernel implementation. But in combination with threaded GHC it makes not working. Also is there any workaround possible in Haskell/GHC? For example making time while openFd is in progress without interrupts? I have found very similar bug reported here: https://bugzilla.redhat.com/show_bug.cgi?id=161314 but code from the patch does not seem to be included in official kernel source code (but it is also a long time ago so many things have probably changed). But the workaround mentioned there is working also here. If I open /dev/rfcomm0 with some other program (so that Bluetooth connection is made) before I run Haskell program then it works in both cases, with or without -threaded option. Of course this is not really useful workaround in my case, I would like to make a stand-alone Haskell program. So if it is similar to that bug then maybe it is a bug in Linux kernel. So please help me solve this problem. Mitar