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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c++,arrays,string,qt,random

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mysql,qt,ubuntu,mariadb

It was a problem with the database and not the Qt application, the connection refused if a password was used.

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c++,qt,qpainter,qheaderview

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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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qt,qml,qt5,user-agent,qtwebengine

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image,qt,qlistwidget,qlistwidgetitem

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json,qt,pyside,animated-gif

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qt,user-interface,adc

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c++,qt

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

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qt,opencv,mingw

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c++,qt

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c++,xml,qt

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c++,qt

There is an example delivered with Qt. Take a look at xmlpatterns/filetree example. It is not that easy as with some other models. You have to implement these abstract methods: QUrl QAbstractXmlNodeModel::documentUri(const QXmlNodeModelIndex &) const QXmlNodeModelIndex::NodeKind QAbstractXmlNodeModel::kind(const QXmlNodeModelIndex &) const QXmlNodeModelIndex::DocumentOrder QAbstractXmlNodeModel::compareOrder(const QXmlNodeModelIndex &,const QXmlNodeModelIndex &) const QXmlNodeModelIndex QAbstractXmlNodeModel::root(const...

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qt,qml

Actually, the page does say how to work around this: If the onCompleted handler instead had "car = new Object({wheels: 6})" then the text would be updated to say "The car has 6 wheels", since the car property itself would be changed, which causes a change notification to be emitted....

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c++,qt,toolbar

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python,qt,pyqt,pyqt4,system-tray

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python,qt

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qt,qslider

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qt,qstring,qfile

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c++,qt,memory-management

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c++,qt,networking

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qt,text,word-wrap,qgraphicsitem

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c++,qt

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c++,qt,qcombobox

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

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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

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qt,qmainwindow

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c++,qt,ftp,qnetworkreply

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

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qt,qwidget,qlabel

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c++,qt,exception

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database,qt,sqlite

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c++,qt

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c++,qt,qmediaplayer,qdir,qfileinfo

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qt,qml,qtquick2,qt-quick

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c++,qt,clipboard

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c,signals

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c++,qt,qstring

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bash,signals

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qt,qt5

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android,qt,deployment,qml,qt5.4

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c++,qt

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

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c++,qt,connect,signals-slots

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

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