How to run valgrind for the server? - c++

Question

I am new to valgrind. I need to run the valgrind for a server written in C++. The server listens to a port. When the run the server inside the Valgrind, I couldn't communicate with the server. The Port is not listening.
valgrind --tool=memcheck --leak-check=yes --log-file=valgrind_log.txt /binary_path-c
I need the server should listen to the port when i run with valgrind.

Answer 1

If you have already confirmed that the exact same binary is doing that desired network socket open() and it doesn’t work in Valgrind, then read on.
Valgrind only works with binary file and cannot attach to an already running process (as explained here).
Valgrind is also sensitive to change of effective UID, particularly when running from root UID. You cannot use sudo with valgrind (detailed here).
You cannot Valgrind on an executable binary that has Linux capability bit enabled (details here).
Valgrind cannot handle root setuid on NFS filesystem (even when mounted to allow this). Workaround is to move your build or binary to non-NFS partition.
Having said all that above, it is a timing problem where Valgrind is taking things SLOWER and that the control flow of your code is “missing its mark” to performing that open to a network socket. Only way is to put in debug print statements throughout your code and nail that timing logic.
Alternatively...
To see what a production grade daemon is doing from the very beginning of startup, execute:
valgrind --trace-children=yes /usr/skin/<your-server-binary>
There’s another way to monitor network socket in action, read on ...
Tracing from start of execution
You can perform strace from the start and find out what network socket got opened (and described later, show its buffer content) by:
strace -eopen <your-server-binary> <server-arguments>
make a note of the desired fd (file descriptor) number.
As with any strace command in starting a process, pressing Ctrl-C will stop that process. But using strace on a live process, you safely detach using Ctrl-C from its targeted process (and let that process continue running) and return to your command shell prompt.
Attaching to already running server
But you could monitor an already running production daemon server using strace but it’s harder to find that opened fd number for your network socket. Do previous step briefly to get that fd.
Find out your PID using ps auxw.
Then plug in your server/daemon’s PID here:
strace -f -p <your-server-PID -fnetwork
to find out its fd number.
Exact socket monitoring
With the identified fd on hand, rerun strace to attach to that production server with:
strace -f -eread=<fd> -ewrite=<fd> -p<your-daemon-PID>
network troubleshooting checklist
lsof -i -n a list of open ports
strace
netstat -lt
tcpdump/wireshark
A list of network troubleshooting tools for Linux is given here, here and most comprehensively here.