Fix tcpkill detection method
diff --git a/perf-scripts/flow-sync-perf.py b/perf-scripts/flow-sync-perf.py
index b782333..61a204b 100755
--- a/perf-scripts/flow-sync-perf.py
+++ b/perf-scripts/flow-sync-perf.py
@@ -35,7 +35,9 @@
print "ONOS Log File:", ONOS_LOG
# Verify that tcpkill is installed
-if not Popen( 'which tcpkill', stdout=PIPE, shell=True).communicate():
+tcpkill_check = Popen( 'which tcpkill', stdout=PIPE, shell=True)
+tcpkill_check.communicate()
+if tcpkill_check.returncode != 0:
print '* Installing tcpkill'
call( 'apt-get install -y dsniff', stdout=PIPE, shell=True )