well, I have a usr1 signal handler in a script. By sending a SIGUSR1 from outside to my script, my handler does its work, but the signal is spread also to the child that I create via Popen. How can I do this?
The rsync manual page says that exit code 20 means:
Received SIGUSR1 or SIGINT
So if you are killing it with kill (not kill -15 which you say you sometimes use) then it would die with this exit code too.
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How do I shut down a python simpleHTTPserver?
(9 answers)
Closed 7 years ago.
I've started a SimpleHTTPServer via the command python -m SimpleHTTPServer 9001.
I'd like to stop it without having to force quit Terminal. What's the keystrokes required to stop it?
CTRL + C is usually the right way to kill the process and leave your terminal open.
Use CTRL+C.
This is a filler text because answer must be 30 characters.
Agree with Ctrl-C answer. Note that pressing Ctrl-C sends 'interrupt' signal (signal number 2).
Alternatively you can use TERM signal to terminate your server process.
You can send 'INT' or 'TERM' signal to request termination. Typically all good programs honor int and term signal and do cleanup.
To terminate a process properly, run
kill -2 <pid>
kill -15 <pid>
or
kill -INT <pid>
kill -TERM <pid>
There is a difference in SIGINT and SIGTERM. From this quora article,
SIGINT is the interrupt signal. The terminal sends it to the foreground process when the user presses ctrl-c. The default behavior is to terminate the process, but it can be caught or ignored. The intention is to provide a mechanism for an orderly, graceful shutdown.
SIGTERM is the termination signal. The default behavior is to terminate the process, but it also can be caught or ignored. The intention is to kill the process, gracefully or not, but to first allow it a chance to cleanup.
So use the right signal depending on your needs.
I have a Python 2.7 multiprocessing Process which will not exit on parent process exit. I've set the daemon flag which should force it to exit on parent death. The docs state that:
"When a process exits, it attempts to terminate all of its daemonic child processes."
p = Process(target=_serverLaunchHelper, args=args)
p.daemon = True
print p.daemon # prints True
p.start()
When I terminate the parent process via a kill command the daemon is left alive and running (which blocks the port on the next run). The child process is starting a SimpleHttpServer and calling serve_forever without doing anything else. My guess is that the "attempts" part of the docs means that the blocking server process is stopping process death and it's letting the process get orphaned as a result. I could have the child push the serving to another Thread and have the main thread check for parent process id changes, but this seems like a lot of code to just replicate the daemon functionality.
Does someone have insight into why the daemon flag isn't working as described? This is repeatable on windows8 64 bit and ubuntu12 32 bit vm.
A boiled down version of the process function is below:
def _serverLaunchHelper(port)
httpd = SocketServer.TCPServer(("", port), Handler)
httpd.serve_forever()
When a process exits, it attempts to terminate all of its daemonic child processes.
The key word here is "attempts". Also, "exits".
Depending on your platform and implementation, it may be that the only way to get daemonic child processes terminated is to do so explicitly. If the parent process exits normally, it gets a chance to do so explicitly, so everything is fine. But if the parent process is terminated abruptly, it doesn't.
For CPython in particular, if you look at the source, terminating daemonic processes is handled the same way as joining non-daemonic processes: by walking active_children() in an atexit function. So, your daemons will be killed if and only if your atexit handlers get to run. And, as that module's docs say:
Note: the functions registered via this module are not called when the program is killed by a signal not handled by Python, when a Python fatal internal error is detected, or when os._exit() is called.
Depending on how you're killing the parent, you might be able to work around this by adding a signal handler to intercept abrupt termination. But you might not—e.g., on POSIX, SIGKILL is not intercept able, so if you kill -9 $PARENTPID, this isn't an option.
Another option is to kill the process group, instead of just the parent process. For example, if your parent has PID 12345, kill -- -12345 on linux will kill it and all of its children (assuming you haven't done anything fancy).
I have a simple example:
from twisted.internet import utils,reactor
def test:
utils.getProcessOutput(executable="/bin/sleep",args=["10000"])
reactor.callWhenRunning(test)
reactor.run()
when I send signal "TERM" to program, "sleep" continues to be carried out, when I press Ctrl-C on keyboard "sleep" stopping. ( Ctrl-C is not equivalent signal TERM ?) Why ? How to kill "sleep" after send signal "TERM" to this program ?
Ctrl-C sends SIGINT to the entire foreground process group. That means it gets send to your Twisted program and to the sleep child process.
If you want to kill the sleep process whenever the Python process is going to exit, then you may want a before shutdown trigger:
def killSleep():
# Do it, somehow
reactor.addSystemEventTrigger('before', 'shutdown', killSleep)
As your example code is written, killSleep is difficult to implement. getProcessOutput doesn't give you something that easily allows the child to be killed (for example, you don't know its pid). If you use reactor.spawnProcess and a custom ProcessProtocol, this problem is solved though - the ProcessProtocol will be connected to a process transport which has a signalProcess method which you can use to send a SIGTERM (or whatever you like) to the child process.
You could also ignore SIGINT and this point and then manually deliver it to the whole process group:
import os, signal
def killGroup():
signal.signal(signal.SIGINT, signal.SIG_IGN)
os.kill(-os.getpgid(os.getpid()), signal.SIGINT)
reactor.addSystemEventTrigger('before', 'shutdown', killGroup)
Ignore SIGINT because the Twisted process is already shutting down and another signal won't do any good (and will probably confuse it or at least lead to spurious errors being reported). Sending a signal to -os.getpgid(os.getpid()) is how to send it to your entire process group.
How we can hook up a code inside a python process so that it should send an alert in case of shutdown of process/abrupt termination ?
Use Supervisor Daemon
It's not clear what exactly you mean. Shutdown/abort of the process itself? Or of a child process?
Shutdown/abort of a process itself: Have a look at Pythons atexit module; here you can register a callback for when your program cleanly exits. But there is absolutely no way for you to catch all circumstances, if your program fails b/o a serious issue (e.g. segfault) your atexit handlers will never get called. You need a supervising process to catch absolutely all aborts.
Shutdown/abort of a child process: If you e.g. use the subprocess module you can simply call poll() or wait() on popen objects to see if the spawned process is dead / wait for them to die. For a more advanced implementation use Pythons signal module to set a handler for SIGCHLD - this signal is sent to your process whenever one of the child processes terminates.
When using mpirun, is it possible to catch signals (for example, the SIGINT generated by ^C) in the code being run?
For example, I'm running a parallelized python code. I can except KeyboardInterrupt to catch those errors when running python blah.py by itself, but I can't when doing mpirun -np 1 python blah.py.
Does anyone have a suggestion? Even finding how to catch signals in a C or C++ compiled program would be a helpful start.
If I send a signal to the spawned Python processes, they can handle the signals properly; however, signals sent to the parent orterun process (i.e. from exceeding wall time on a cluster, or pressing control-C in a terminal) will kill everything immediately.
I think it is really implementation dependent.
In SLURM, I tried to use sbatch --signal USR1#30 to send SIGUSR1 (whose signum is 30,10 or 16) to the program launched by srun commands. And the process received signal SIGUSR1 = 10.
For platform MPI of IBM, according to https://www.ibm.com/support/knowledgecenter/en/SSF4ZA_9.1.4/pmpi_guide/signal_propagation.html
SIGINT, SIGUSR1, SIGUSR2 will be bypassed to processes.
In MPICH, SIGUSR1 is used by the process manager for internal notification of abnormal failures.
ref: http://lists.mpich.org/pipermail/discuss/2014-October/003242.html>
Open MPI on the other had will forward SIGUSR1 and SIGUSR2 from mpiexec to the other processes.
ref: http://www.open-mpi.org/doc/v1.6/man1/mpirun.1.php#sect14>
For IntelMPI, according to https://software.intel.com/en-us/mpi-developer-reference-linux-hydra-environment-variables
I_MPI_JOB_SIGNAL_PROPAGATION and I_MPI_JOB_TIMEOUT_SIGNAL can be set to send signal.
Another thing worth notice: For many python scripts, they will invoke other library or codes through cython, and if the SIGUSR1 is caught by the sub-process, something unwanted might happen.
If you use mpirun --nw, then mpirun itself should terminate as soon as it's started the subprocesses, instead of waiting for their termination; if that's acceptable then I believe your processes would be able to catch their own signals.
The signal module supports setting signal handlers using signal.signal:
Set the handler for signal signalnum to the function handler. handler can be a callable Python object taking two arguments (see below), or one of the special values signal.SIG_IGN or signal.SIG_DFL. The previous signal handler will be returned ...
import signal
def ignore(sig, stack):
print "I'm ignoring signal %d" % (sig, )
signal.signal(signal.SIGINT, ignore)
while True: pass
If you send a SIGINT to a Python interpreter running this script (via kill -INT <pid>), it will print a message and simply continue to run.