``pt-stalk` with ``--mysql-only`` option was not adding MySQL ``processlist`` information to the output file.

mysql-only option is not working as expected.

By running :

/usr/bin/pt-stalk --host 127.0.0.1 --port 3355 --mysql-only --daemonize --log /tmp/pt-stalk/pt-stalk.log --dest /tmp/pt-stalk --function status --variable Threads_running --threshold 12 --cycles=10 --sleep=30 --run-time=20 --interval 5 --retention-time 1 --disk-pct-free 10

The generated file :

/tmp/pt-stalk/2018_07_03_14_30_22-processlist  is empty.

Only  by removing mysql-option, the file is populated.

I'am using 5.5.59-38.11-log Percona Server (GPL), Release 38.11, Revision 2084a7bc7ec version runnig on centos 6.9.

Kernel version :  2.6.32-696.20.1.el6.x86_64 #1 

Also, on my box, other mysql istances ( listening on different ports ) are running.

Thanks.