I'm using Ubuntu 14.04, gnuradio 3.7.8, USRP N210 and the latest UHD. Everything was recently (3 days ago) updated to newest versions and USRP's reflashed. I have custom flowgraphs that use the USRP N210's that work fine.
I decided to play around with the benchmark_tx and benchmark_rx scripts to see what they could do, but I'm not able to receive anything because a segmentation fault crashes the benchmark_rx script as soon as I start the tx script. Even with the -v flag, I don't get any error output other then 'Segmentation fault (core dumped)'.
Here is an example of the commands I use to start the scripts. I start the rx and then the tx.
TX: ./benchmark_tx.py -v -f 1000000000 -r 800000 --args="addr=10.0.8.5" -A TX/RX --tx-gain=15
RX: ./benchmark_rx.py -v -f 1000000000 -r 800000 --args="addr=10.0.8.4" -A RX2 --rx-gain=15