# Issue with Virtual Sink/Source **URL:** \ **Category:** GNU Radio\ **Created:** [January 5, 2015, 5:58pm UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712 "2015-01-05T17:58:16Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [January 5, 2015, 5:58pm UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/1 "2015-01-05T17:58:16Z")
Hi, We recently bought a new PC with some powerful specs. GNU Radio was built from the source and it seems to be installed fine. However, when I try to use the virtual sink and source blocks in my flow graph, I am getting the following error: Traceback (most recent call last): File “./test\_skh.py”, line 595, in tb = test\_skh() File “./test\_skh.py”, line 486, in **init** self.connect((self.virtual\_source\_0, 0), (self.blocks\_multiply\_conjugate\_cc\_0, 0)) File “/usr/local/lib/python2.7/dist-packages/gnuradio/gr/hier\_block2.py”, line 93, in **getattr** return getattr(self.\_impl, name) _AttributeError: ‘top\_block\_sptr’ object has no attribute ‘virtual\_source\_0’_ Once I replace the virtual blocks with direct connections, things work just fine. What is the cause for this problem and how to fix it? Please note that on an older machine, GNU Radio was installed around a month ago following the same procedure followed here, and the virtual sink/source blocks work just fine. Thank you. Best regards, Khalid ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 5, 2015, 6:12pm UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/2 "2015-01-05T18:12:32Z")
On 01/05/2015 11:57 AM, khalid.el-darymli wrote: > File “./test\_skh.py”, line 486, in **init** > Once I replace the virtual blocks with direct connections, things work > > * * * > > Discuss-gnuradio mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) > My guess is that this machine has GR installed from the official repos > as well, and you’re getting an old GR instance. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 12, 2015, 11:26pm UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/3 "2015-01-12T23:26:56Z")
Hi, I’m having the same issue as Khalid. I just updated my GNU Radio source based installation on two different machines. On one of the machines I previously had a source installation of gnuradio 3.7.4. This machine runs Linux Mint 17.1, the other machine runs Ubuntu 14.04. A flow graph utilising virtual sources and sinks that ran fine under gnuradio and gnuradio-companion 3.7.4 now throws up the same error as Khalid has pointed out, on both my Linux Mint and Ubuntu machines. Anyone else seeing this behaviour? Any ideas? Thanks Cheers Richard On 6 January 2015 at 05:57, khalid.el-darymli [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 13, 2015, 2:45am UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/4 "2015-01-13T02:45:08Z")
* * * Discuss-gnuradio mailing list removed\_email\_address@domain.invalid [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 13, 2015, 2:52am UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/5 "2015-01-13T02:52:54Z")
* * * Discuss-gnuradio mailing list removed\_email\_address@domain.invalid [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 13, 2015, 2:02pm UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/6 "2015-01-13T14:02:03Z")
Thanks Johnathan for the update. BTW, with the recent installation, I am also getting the following warning when running my GRC or the GRC-generated python script, fft\_impl\_fftw: /home/ov/.gr\_fftw\_wisdom: Permission denied fft\_impl\_fftw: /home/ov/.gr\_fftw\_wisdom: Permission denied fft\_impl\_fftw: /home/ov/.gr\_fftw\_wisdom: Permission denied . . . fft\_impl\_fftw: /home/oceanview/.gr\_fftw\_wisdom: Permission denied This warning is repeated in the terminal like 100 times before the script actually runs. I am not sure why? Thanks. Best regards, Khalid On Mon, Jan 12, 2015 at 10:21 PM, Johnathan C. \ **Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 13, 2015, 2:18pm UTC](https://www.ruby-forum.com/t/issue-with-virtual-sink-source/233712/7 "2015-01-13T14:18:19Z") Hi, > fft\_impl\_fftw: /home/oceanview/.gr\_fftw\_wisdom: Permission denied > > This warning is repeated in the terminal like 100 times before the script > actually runs. I am not sure why? Erase that file. My guess is that it was created when something was run as root and now you can’t write to it as a normal user. Cheers, Sylvain