I run a python script using urllib2 to collect some data from various online APIs. Everything seems to run smoothly when sudenly the script starts to hang and becomes unresponsive (CTRL+C does not have any effect). I open a new shell to see what's going on and I notice that any application that triggers a network activity starts to hang (yum, pip...). I open my TTY console and I notice that some error messages are popping : "eth0: Detected Tx Unit Hang", "eth0 Reset Adapter" and something about kernel hang timeout... A lot of signs that something really bad is happening on this machine. The only way to recover from it consists in performing a hardware reset of the Guest machine, but the problem arises again shortly after.
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| Screenshot of the situation |
The issue had nothing to do with my script or my VM setup, but was in the configuration of the VirtualBox instance. I have a Intel i7-2600 CPU with 4 cores on my Host, so I though it was a good idea to assign multiple cores to my VM to improve performances and to have something closer to my production server. Turns out that by doing this I caused the problem: assigning more than 1 cpu to my VM results in the network interface to hang and freeze the kernel after a certain amount of data is transmited. I'm using the last version of Virtualbox to date (4.2.4) with Centos (6.3). Hopefully this will be fix in the next release.
TL;DR: If your VM is hanging and shows some network errors, check how many CPU you assigned to it, and if this is more than one, reduce it.
I posted this fix in English because I ran into this annoying situation and I wanted it to be available to more than my usual French audience, considering I didn't find that much info about it except this old entry in Virtualbox bugtracker.
