I'm in a computer networking class and I am writing a simple server that just sends and receives messages from the client (which is given). However my server is getting segmentation faults when the given client connects. How can I run GDB to debug this? I try running the server with gdb but it just hangs because there is an infinite while loop in my server and I don't know how to run the client simultaneously to trigger the segfault. Can anyone help?
I don't know how to run the client simultaneously to trigger the segfault.
Simple: you open another window, and run the client from there.
If your server spawns (fork()) separate process for each connected client, you probably need to set follow fork mode: http://www.delorie.com/gnu/docs/gdb/gdb_26.html
"set follow-fork-mode child" will start debugging of the spawned process right after accept() and fork().
Another option is to analyze the core file. Coredumps are mostly disabled by default, so you need to enable them:
ulimit -c unlimited
Run your server, let it segfault and start gdb pointing it to core and your binary:
gdb -c ./core.xxxx ./server
Related
If I run a website using a http_deamon on a server is it possible to ssh into the server then open the prolog interface, run some queries, notably make and close the interface with the website still running?
Yes, it's possible to reload definitions with a running HTTP server.
Steps to reproduce:
Start a screen or tmux session. This lets you detach the terminal to log in later into the same session.
Start the server. With the HTTP daemon library, use the --interactive flag to get an interactive toplevel.
Detach the session.
Log out.
At any later time, to reload definitions while the server is still running, simply:
log in again
re-attach the session
run ?- make. as usual.
Caveat: With the HTTP Unix daemon, make/0 currently some issues, but you can always start an HTTP server also without using the http_unix_daemon library, and in that case make/0 works more nicely.
An alternative is to simply provide a special URL handler that runs make/0 within the server when that URL is accessed. Again, it may not work smoothly with the Unix daemon library, but typically when run without it.
i've got problem with tuxedo tmshutdown command. One of processes still runs (with huge cpu usage) though tmshutdown stops it succesfull. There is also one opened IPC shared memory which i can close when I kill existing process. There are other servers but only this one is problematic. Is it possible that the problem is in code (tpsvrdone is exiting without errors)?
Tmshudown normally sends a SIGTERM signal to tuxedo serves unless you use -k KILL (which sends a SIGKILL)
If the source code of the Tuxedo server implements a handler of the signal, you could get the behavior you explained.
http://www.thegeekstuff.com/2012/03/catch-signals-sample-c-code/
Also, if it is not possible to shutdown a server, or remove a service advertisement, a diagnostic is written on the ULOG.
Our group has long running processes which run daily. The processes are typically started at 9pm on any given day and run until 7pm the next day. Thus they typically run 22hrs/day. They are started by scheduled tasks on servers under a particular generic user ID, and they start and run regardless of whether or not that user ID is logged on. Thus, they are windowless console executables.
The tasks orchestrate computations running on a large server farm. Generally these controlling tasks run uninterrupted for the full 22hrs/day. However, we often have a need to stop and restart these processes. Because they control a multitude of tasks running on our server farm, it is important that they be shut down cleanly, so that they can stop and shut down all the server farm processes. Which brings me to our problem.
The controlling process has been programmed to respond to ctrl-C and ctrl-break signals. This works fine when the process is manually started in a console where we have access to the console and can "type" ctrl-c or ctrl-break in the console window. However, as mentioned, the processes typically run as windowless scheduled tasks. Hence we cannot "type" anything into a non-existent console window. Because they are console processes that execute without a logon process, the also must be able to execute in a completely windowless environment. So, how do we set up the process to listen for a shut-down signal?
While the process does indeed listen for a ctrl-C and ctrl-break signal, I can see no way to send that signal to a process. This seems to be a fundamental problem in Windows, or am I wrong? I am aware of SendSignal.exe, but so far have been unable to get it to work. It fails as follows:
>SendSignal 26320
Sending signal to process 26320...
CreateRemoteThread failed with 0x00000005.
StartRemoteThread failed with 0x00000005.
0x00000005 == Access is denied.
Trying "taskkill" without -F results in:
>taskkill /PID 24840
ERROR: The process with PID 24840 could not be terminated.
Reason: This process can only be terminated forcefully (with /F option).
All other "kill" functions kill the process immediately rather than sending a signal.
One possible solution would be a file-watch based solution: create a watch for some modification of a specific file. But this is a hack and we would prefer to do it with appropriate signaling. Has anyone solved this issue? It seems to be so very basic a functionality, and it is certainly trivial to do it in a Unix environment. Surely Microsoft has provided SOME mechanism to allow clean shut down of a windowless executable?
I am aware of the thread below, whose question is virtually identical (save for the specification of why the answer is necessary, i.e. why one needs to be able to do this for a windowless, console-less process), but there is no answer there excpet for "use SendSignal", which, as I said, does not work for us:
Can I send a ctrl-C (SIGINT) to an application on Windows?
There are other similar questions, but no answers as yet.
Any help appreciated.
[Upgrading #Anon's comment to an answer for visibility]
windows-kill worked perfectly and managed to resolve access denial issues faced with SendSignal. A privileged user would have to run it as well of course.
windows-kill also supports both ctrl-c and ctrl-break signals.
Update: We are using AIX environment.
We have been facing some random issues with our queues (cluster queues), like:
2189 Cluster resolution error (Most frequent one)
2270 MQRC_NO_DESTINATIONS_AVAILABLE
2053 Queue full error(Weirdest) : Post one message, it will be successfully posted, post some 3-4 messages, it will throw this error
for the rest of the messages.
All these issues get resolved once we do a cluster refresh. But, I want to know the root cause, why we get these errors. What goes wrong?
How cluster refresh resolve these errors?
Could be a socket issue. You can monitor sockets according to your OS - like on windows can do
netstat -a -b -o >/newfile.txt
You could also use TCP Viewer on windows (one exe from Microsoft/ sysinternals) http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx actually all the sys internal toos should be in your prod box if windows.
For sockets in linux/Un* there are other tools, some just ls commands into the RAM, depending on the version. Maybe a google will help.
Also if using windows consider moving some stuff to linux, you will have some pain in the beggining but will get better.
If this did not help you should post yor environment on your quesiton and give any other details. And if you get a jprofiler into production and use it when the issue happens.
At the very least you can do a jstack and jmap
What is version/ name of OS and of java, websphere?
If it is a socket issue can try increasing sockets (registry) and then profiling your code to see who is making too many sockets, what needs to be throttled or re-written.
Remember every page, every db connection, external cache hit (if you use) or any other URL work/ remote connection is usually a socket.
I have a single instance of InDesign Server running on a Windows 2007 VPS, which runs a SOAP service on port 8081. This runs as a Windows Service and runs both dev and live JSX scripts, depending on the path of the script (we have a dev folder and a live folder).
I am having trouble running a new script, so would like to get access to the console of the running service, but I am struggling to find a reference to how to do this in the Adobe PDF docs. I know the script itself being found, since there are errors in the Windows Event Viewer for a specific code line, but I think it is having trouble locating JSXBIN resources. The error message just lists the variable in question, rather than the explicit path.
I have modified the script to output path information to stdout, but this doesn't get into the Event Log. So, can I get a window on the console of the running service? I don't want to stop the current service as that is in use for live.
Some ideas I've got from the docs:
InDesignServer -console
InDesignServer -LogToApplicationEventLog
I think this executable however starts up a new instance, which isn't what I want (either it would choose a new port number, or try with 8081 and fail to start since the port is in use - I've not tried either for obvious reasons). The flags respectively display stdout in the DOS window, and redirect std out to the Event Log.
In short, I don't think this is possible. I was hesitant to start a new instance on our live server in case it upset anything, but in fact it is quite safe; just ensure that the port you specify is different to your usual one.
InDesignServer -noconsole -port 10001
The noconsole connects stdout and stderr with the current DOS window - using console opens a new one, so it's the former you want.
Aside: it may be worth avoiding LogToApplicationEventLog, since the process can get disconnected from the console, which makes it fiddly to kill in a graceful manner.