Qt app receives HUP signal unexpectedly when forked to background

Tag: qt,signals,fork,daemon,signals-slots

I have built a Qt app which upon receipt of the HUP signal shuts down nicely (setup like this how to get signals into Qt). This works great under Red Had 6, but when I run this app under Ubuntu 14 my app receives the HUP signal immediately (after forking to run in the background) and then shuts down - even though I didn't send a HUP. Furthermore, this ONLY happens when my app forks and runs in the background - if I run my app in the foreground it does not receive the hup unexpectedly.

Is there some other reason that might cause it to receive a HUP signal when daemonized? (And why under one distro but not the other)

Best How To :

When daemonizing (forking), the parent process issues a HUP signal upon exit. For some reason on Red Hat this signal doesn't hit child process until much later. On Ubuntu the signal hits the child quickly (or perhaps Ubuntu holds the signal for the child).

Solution is to confirm parent process has terminated and then hook into the HUP signal.

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qt,qslider

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c++,qt,clipboard

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python,qt,pyqt,pyqt4,system-tray

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qt,qml,qt5,user-agent,qtwebengine

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c++,qt,qmediaplayer,qdir,qfileinfo

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c++,qt

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c++,sql-server,qt,tsql,odbc

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c++,osx,qt,fsevents,file-watcher

The problem was unrelated to this code. The pointer works fine but his object was lost.

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database,qt,sqlite

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qt,text,word-wrap,qgraphicsitem

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c++,qt,memory-management

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c++,qt

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qt,user-interface,python-3.x,dialog,qt-creator

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Bash ERR signal not trapped in procedures?

bash,signals

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c++,qt

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c++,qt

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qt,qdatetime

Your date string does not include a time, while you mentioned that you want one, this will fail at least in Qt 5.4 . I don't know though why you get the epoche outputed, maybe that is dependant on your Qt version. Your date format is also locale dependent. See...

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c++,qt,toolbar

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mysql,qt,ubuntu,mariadb

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QT-FTP Upload Error

c++,qt,ftp,qnetworkreply

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c++,qt,qcombobox

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qt,qml

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qt,qmainwindow

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c++,qt

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c++,qt,inheritance,overloading,operator-keyword

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c++,qt

The issue is with following signal slot connection. QObject::connect(calculate, SIGNAL(clicked()), &prog, SLOT(results->setNum(value(*spinner));)); You are trying to connect the clicked() signal of calculate button to results->setNum(value(*spinner)); slot of prog. But results->setNum(value(*spinner)); is not actually a slot. A slot is simply a method in a class that inherits QObject. Method should be...

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c++,c,linux,signals,posix

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c,signals

Historically, lots of details about how signals work have changed. For instance, in the earliest variant, the processing of the signal reverted to default when the handler was called, and the handler had to re-establish itself. In this situation, sending the signal from the handler would kill the process. Currently,...

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qt,user-interface,adc

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c++,qt,exception

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c++,qt,sorting,c++11

You can make a map between their choice and a functor to sort by, for example using SortFun = bool(*)(Hotel const&, Hotel const&); std::map<char, SortFun> sorters { {'s', [](Hotel const& lhs, Hotel const& rhs){ return lhs.stars < rhs.stars; }}, {'f', [](Hotel const& lhs, Hotel const& rhs){ return lhs.freeRoomCount < rhs.freeRoomCount;...

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qt,qwidget,qlabel

I would override MonitoringWidget::paintEvent() and then use the monitored widget's QWidget::render() to render the monitored widget into the MonitoringWidget. This should roughly be equivalent to what the widget being monitored itself will do when it receives paint events. Also you probably need some link between the monitored widget and the...

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qt,qt5

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qt,opencv,mingw

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json,qt,pyside,animated-gif

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c++,qt,connect,signals-slots

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c++,arrays,string,qt,random

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c++,qt,networking

If aborted, QNetworkReply::error() should return QNetworkReply::OperationCanceledError, which means: the operation was canceled via calls to abort() or close() before it was finished. ...

Plotting random signal on circle

matlab,plot,signals,circle

You need to add "noise" to the radius of the circle, roughly around r=1: th = linspace( 0, 2*pi, N ); %// N samples noise = rand( 1, N ) * .1; %// random noise in range [0..0.1] r = 1+noise; %// add noise to r=1 figure; plot( r.*cos(th), r.*sin(th)...

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c++,xml,qt

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qt,qml,qtquick2,qt-quick

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android,qt,deployment,qml,qt5.4

When deploying the application, androiddeployqt will copy a bunch of files which terribly fails on Windows when source or destination paths become longer than 260 characters (yeah, that's a "known feature"). Keeping the Qt installation and the project directory as top level as possible helps to reduce the path lengths...

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qt,qstring,qfile

QString selected = model2->filePath(index); does not set the variable in the (maybe same named) member OptionsDialog::selected. This creates a new local variable. If you have a member variable called selected then you should use it like this: void OptionsDialog::getData(const QModelIndex &index) { selected = model2->filePath(index); ... } ...

Using QSimpleXmlNodeModel and QTreeView

c++,qt

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change QDir::rootPath() to program running path?

c++,qt

QCoreApplication::applicationDirPath() returns the exact directory path of your app, for example H:/programs if your app path is H:/programs/ftpserver.exe so if you modify that QString you can get the root dir. For example: QString rootPath = QCoreApplication::applicationDirPath(); rootPath.chop(rootPath.length() - 3); //we leave the 3 first characters of the path, the root...

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c++,qt,qpainter,qheaderview

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Qstring error. Saving from Textpool to string

c++,qt,qstring

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qt,qml,qtquick2

States are a way to represent different property configurations for a given Item. Each State has its unique set of values for the properties defined inside the specific Item. Transitions are a way to add animations to an Item when the current State changes to another State. They can be...

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image,qt,qlistwidget,qlistwidgetitem

Use QImage first to scale the image and construct the icon from the resulting pixmap. QSize desiredSize; Qimage orig(filesToLoad[var]); Qimage scaled = orig.scaled( desiredSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation); QListWidgetItem *listItem = new QListWidgetItem(QIcon(Qpixmap::fromImage(scaled)),filename); It is very common to store the presized image too on the disk, to avoid the two step conversion...

Rotating a Label In Qt with Python

python,qt

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