|Note: This tutorial assumes that you have completed the previous tutorials: Using rxconsole and roslaunch.|
|Please ask about problems and questions regarding this tutorial on answers.ros.org. Don't forget to include in your question the link to this page, the versions of your OS & ROS, and also add appropriate tags.|
How to Roslaunch Nodes in Valgrind or GDBDescription: When debugging roscpp nodes that you are launching with roslaunch, you may wish to launch the node in a debugging program like gdb or valgrind instead. Doing this is very simple.
Keywords: roslaunch, valgrind, gdb, pdb
Tutorial Level: INTERMEDIATE
The launch-prefix attribute of the <node> tag that, among other things, makes it easy to debug a ROS node process. Here are some example launch-prefixes you might find useful:
launch-prefix="xterm -e gdb --args" : run your node in a gdb in a separate xterm window, manually type run to start it
launch-prefix="gdb -ex run --args" : run your node in gdb in the same xterm as your launch without having to type run to start it
launch-prefix="valgrind" : run your node in valgrind
launch-prefix="xterm -e" : run your node in a separate xterm window
launch-prefix="nice" : nice your process to lower its CPU usage
launch-prefix="screen -d -m gdb --args" : useful if the node is being run on another machine; you can then ssh to that machine and do screen -D -R to see the gdb session
launch-prefix="xterm -e python -m pdb" : run your python node a separate xterm window in pdb for debugging; manually type run to start it
launch-prefix="/path/to/run_tmux": run your node in a new tmux window; you'll need to create /path/to/run_tmux with the contents:
#!/bin/sh tmux new-window "gdb --args $*"
Obtaining core dumps
To obtain core dumps when processes crash, first set the core file size limit. To check the limits, run:
$ ulimit -a core file size (blocks, -c) 0 # <-- Prevents core dumps data seg size (kbytes, -d) unlimited scheduling priority (-e) 20 file size (blocks, -f) unlimited pending signals (-i) 16382 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) unlimited virtual memory (kbytes, -v) unlimited file locks (-x) unlimited
Set the core size to unlimited:
ulimit -c unlimited
Now crashing processes will attempt to create core files. Currently (2010-07-02) they will fail to create the file because the default roslaunch working directory, $ROS_HOME, contains a directory named "core". This directory prevents the core dump from being created.
To allow core dumps to be created, set the core filename to use the process pid by default. Run the following as root:
echo 1 > /proc/sys/kernel/core_uses_pid
Now core dumps will show up as $ROS_HOME/core.PID
If you get error like below one, you should try to launch node in another windows with gdb.link
launch-prefix="xterm -e gdb --args"
[tcsetpgrp failed in terminal_inferior: Inappropriate ioctl for device]