Questions tagged [signals]
A signal is a notification to a process that an event occurred. Signals are sometimes described as software interrupts. Signals are analogous to hardware interrupts in that they interrupt the normal flow of execution of a program; in most cases, it is not possible to predict exactly when a signal will arrive. They are defined in the C standards and extended in POSIX, but many other programming languages/systems provide access to them as well.
signals
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What killed my process and why?
My application runs as a background process on Linux. It is currently started at the command line in a Terminal window.
Recently a user was executing the application for a while and it died ...
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How do I capture SIGINT in Python?
I'm working on a python script that starts several processes and database connections. Every now and then I want to kill the script with a Ctrl+C signal, and I'd like to do some cleanup.
In Perl I'd ...
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What's the best way to send a signal to all members of a process group?
I want to kill a whole process tree. What is the best way to do this using any common scripting languages? I am looking for a simple solution.
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How to prevent SIGPIPEs (or handle them properly)
I have a small server program that accepts connections on a TCP or local UNIX socket, reads a simple command and (depending on the command) sends a reply.
The problem is that the client may have no ...
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Is it possible to capture a Ctrl+C signal (SIGINT) and run a cleanup function, in a "defer" fashion?
I want to capture the Ctrl+C (SIGINT) signal sent from the console and print out some partial run totals.
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What is the difference between sigaction and signal?
I was about to add an extra signal handler to an app we have here and I noticed that the author had used sigaction() to set up the other signal handlers. I was going to use signal(). To follow ...
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What is the difference between SIGSTOP and SIGTSTP?
Just wondering about the difference between SIGSTOP and SIGTSTP signals.
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What does `kill -0 $pid` in a shell script do?
Basically, what signal does '0' represent, because here I see SIGNAL numbers starting from 1.
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Signal handling with multiple threads in Linux
In Linux, what happens when a program (that possibly has multiple threads) receives a signal, like SIGTERM or SIGHUP?
Which thread intercepts the signal? Can multiple threads get the same signal? Is ...
user500944
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In what order should I send signals to gracefully shutdown processes?
In a comment on this answer of another question, the commenter says:
don’t use kill -9 unless absolutely
necessary! SIGKILL can’t be trapped so
the killed program can’t run any
shutdown ...
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Can I send a ctrl-C (SIGINT) to an application on Windows?
I have (in the past) written cross-platform (Windows/Unix) applications which, when started from the command line, handled a user-typed Ctrl-C combination in the same way (i.e. to terminate the ...
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How to avoid using printf in a signal handler?
Since printf is not reentrant, it's not supposed to be safe to use it in a signal handler. But I've seen lots of example codes that uses printf this way.
So my question is: when do we need to avoid ...
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How to suspend/resume a process in Windows?
In Unix we can suspend a process execution temporarily and resume it with signals SIGSTOP and SIGCONT. How can I suspend a single-threaded process in Windows without programming ?
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How can I catch SIGSEGV (segmentation fault) and get a stack trace under JNI on Android?
I'm moving a project to the new Android Native Development Kit (i.e. JNI) and I'd like to catch SIGSEGV, should it occur (possibly also SIGILL, SIGABRT, SIGFPE) in order to present a nice crash ...
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Calling pthread_cond_signal without locking mutex
I read somewhere that we should lock the mutex before calling pthread_cond_signal and unlock the mutex after calling it:
The pthread_cond_signal() routine is
used to signal (or wake up) another
...
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Catch Ctrl+C / SIGINT and exit multiprocesses gracefully in python [duplicate]
How do I catch a Ctrl+C in multiprocess python program and exit all processes gracefully, I need the solution to work both on unix and windows. I've tried the following:
import multiprocessing
import ...
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What is the correct way to make my PyQt application quit when killed from the console (Ctrl-C)?
What is the correct way to make my PyQt application quit when killed from the console (Ctrl-C)?
Currently (I have done nothing special to handle unix signals), my PyQt application ignores SIGINT (...
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Django: signal when user logs in?
In my Django app, I need to start running a few periodic background jobs when a user logs in and stop running them when the user logs out, so I am looking for an elegant way to
get notified of a user ...
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Where are core dumps written on Mac?
On Mac OS X, if I send SIGQUIT to my C program, it terminates, but there is no core dump file.
Do you have to manually enable core dumps on Mac OS X (how?), or are they written to somewhere else ...
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POSIX threads and signals
I've been trying to understand the intricacies of how POSIX threads and POSIX signals interact. In particular, I'm interested in:
What's the best way to control which thread a signal is delivered to (...
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Why can't Unix programs have signals with meaningful program defined names (rather than USR1, etc)?
Many Unix programs accept signals like USR1 and USR2. For example, to upgrade the executable for Nginx on the fly, you send kill -USR2.
I understand that USR1 is a "user defined" signal, meaning that ...
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Providing/passing argument to signal handler
Can I provide/pass any arguments to signal handler?
/* Signal handling */
struct sigaction act;
act.sa_handler = signal_handler;
/* some more settings */
Now, handler looks like this:
void ...
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How and why does QuickEdit mode in Command Prompt freeze applications?
I recently ran into an issue with Command Prompt on Windows where QuickEdit mode was enabled and clicking the window was selecting text and hanging a running program. This is, apparently, known ...
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No overload matches this call. Type 'string' is not assignable to type 'Signals'
I am using typescript to build a microservice and handling signals as well. The code was working fine till a few days ago but recently it started throwing errors. Couldn't find a fix for the issue.
...
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How to trap exit code in Bash script
There're many exit points in my bash code. I need to do some clean up work on exit, so I used trap to add a callback for exit like this:
trap "mycleanup" EXIT
The problem is there're different exit ...
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Pusher vs Pubnub vs open source Socket.io / SignalR.net / Faye / jWebSocket [closed]
I'm evaluating Pusher and PubNub at the moment to enable bi-directional realtime communications between my primarily web clients and my servers. Both look impressive, with Pusher's docs seeming to be ...
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Get signal names from numbers in Python
Is there a way to map a signal number (e.g. signal.SIGINT) to its respective name (i.e. "SIGINT")?
I'd like to be able to print the name of a signal in the log when I receive it, however I cannot ...
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How to capture Control+D signal?
I want to capture the Ctrl+D signal in my program and write a signal handler for it.
How can I do that?
I am working on C and using a Linux system.
Ryan
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Android Fatal Signal 11
In the app I'm developing on Android, I keep getting a Fatal Signal 11 error.
I think it's something to do with the way that I'm accessing the memory but I can't figure out what is causing it.
Here's ...
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Run one command after another, even if I suspend the first one (Ctrl-z)
I know in bash I can run one command after another by separating them by semicolons, like
$ command1; command2
Or if I only want command2 to run only if command1 succeeds, using &&:
$ ...
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PyQt4.QtCore.pyqtSignal object has no attribute 'connect'
I'm having issues with a custom signal in a class I made.
Relevant code:
self.parse_triggered = QtCore.pyqtSignal()
def parseFile(self):
self.emit(self.parse_triggered)
Both of those belong to ...
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How to trigger SIGUSR1 and SIGUSR2?
I'm getting acquainted with signals in C. I can't figure out what kind of signals SIGUSR1 and SIGUSR2 are and how can I trigger them. Can anyone please explain it to me?
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How are asynchronous signal handlers executed on Linux?
I would like to know exactly how the execution of asynchronous signal handlers works on Linux. First, I am unclear as to which thread executes the signal handler. Second, I would like to know the ...
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How do I prevent fixtures from conflicting with django post_save signal code?
In my application, I want to create entries in certain tables when a new user signs up. For instance, I want to create a userprofile which will then reference their company and some other records for ...
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Checking if errno != EINTR: what does it mean?
I've found this piece of code used several times (also a similar one where it's used open() instead of write()).
int c = write(fd, &v, sizeof(v));
if (c == -1 && errno != EINTR) {
...
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What is in Apache 2 a "caught SIGWINCH" error?
My server (ubuntu 8.04) LAMP running drupal 6, when there is high traffic, it stops serving pages. A restart of apache2 will not work, so I have to restart the service.
I found this message in the ...
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How to stop 'uninterruptible' process on Linux?
I have a VirtualBox process hanging around which I tried to kill (KILL/ABORT) but without success. The parent pid is 1 (init).
top shows the process as D which is documented as "uninterruptible sleep"...
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Accessing the user's request in a post_save signal
I have done the below post_save signal in my project.
from django.db.models.signals import post_save
from django.contrib.auth.models import User
# CORE - SIGNALS
# Core Signals will operate based ...
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Is Django post_save signal asynchronous?
I have a like function which is just like social networks like or thumbs up function; the user clicks the star / heart / whatever to mark the content as liked.It is done with ajax and must be fast.
...
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How do I mock a django signal handler?
I have a signal_handler connected through a decorator, something like this very simple one:
@receiver(post_save, sender=User,
dispatch_uid='myfile.signal_handler_post_save_user')
def ...
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Signals and interrupts a comparison
Based on various references, my subjective definition of signals in Linux is "The triggers that are used to notify the processes about an occurrence of a specific event.Event here may refer to a ...
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Debugging child process after fork (follow-fork-mode child configured)
I'm developing an application which the parent forks a child to handle certain tasks. I'm having an issue where I've configured gdb to follow-fork-mode child but after fork, after reaching a ...
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Capture SIGINT in Java
What is the best way to capture a kill signal in java without using JNI. I did discover the sun.misc.Signal and the sun.misc.SignalHandler and the warning of the possibility of being removed in the ...
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Is Python variable assignment atomic?
Let's say I am using a signal handler for handling an interval timer.
def _aHandler(signum, _):
global SomeGlobalVariable
SomeGlobalVariable=True
Can I set SomeGlobalVariable without worrying ...
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Under what circumstances are C++ destructors not going to be called?
I know that my destructors are called on normal unwind of stack and when exceptions are thrown, but not when exit() is called.
Are there any other cases where my destructors are not going to get ...
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Python: What is the default handling of SIGTERM?
What does Python do under the covers by default if it receives a SIGTERM but there is no signal handler registered for it?
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Which signal does ctrl-x send when used in a terminal?
On Linux/Unix there are signals. The CtrlC one (SIGINT) is obvious to me.
Now, in some other applications there are signals via CtrlX?!
Is that even a signal or does it generate an escape sequence?
...
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How to send signal to program run in a docker container?
I have a program run in a docker container with detached mode.
So how to send a signal such as SIGINT to this program?
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