Quick summary

A library facilitating the creation of daemons (linux) or services (windows).

Description

There are two exposed classes QDaemonApplication and QDaemonLog.

QDaemonApplication is derived from QCoreApplication and provides the basic infrastructure for the daemon.

QDaemonApplication exposes 5 signals:

daemonized(QStringList) - emitted when the application is started as a daemon/service by the OS and notifies the user that initializations (like connecting signals/slots) can be done. The string list passed is a proper command line (can be used with QCommandLineParser) set for the daemon when installing.
started() - emitted when the application is run as a controlling terminal, notifying the user that the daemon/service has started.
stopped() - emitted when the application is run as a controlling terminal, notifying the user that the daemon/service has stopped.
installed() - emitted when the application is run as a controlling terminal, notifying the user that the daemon/service has been installed.
uninstalled() - emitted when the application is run as a controlling terminal, notifying the user that the daemon/service been uninstalled.

QDaemonLog is the logging component for the daemon. It's set up to output on stdout when the application is run as controlling terminal, and to a file (named after the application with .log extension) when the application is ran as daemon/service. The logging component can be used by the user through QDaemonLog & qDaemonLog(); coupled with QDaemonLog & QDaemonLog::operator << (const QString &) or void qDaemonLog(const QString &, QDaemonLog::EntrySeverity). Currently the format of the output messages is fixed. The QDaemonLog methods (and global functions) are thread-safe.

Dependencies

The library requires Qt 5.6 or later.

Linux: QtCore and QtDBus modules are required

Windows: QtCore + the native libraries AdvApi and User32 (headers and import library files should be provided through the windows SDKs)

Building

Build as any one Qt compatible library (the library make file is called qdaemon.make).

Run qmake and then make -f qdaemon.make/nmake /F qdaemon.make or equivalent.

Running

The application behaviour is controlled through command line switches. When no switches are passed the application tries to run as a daemon. With command line switches the application works as a controlling terminal for the daemon/service.

--start, -s Run the application as controlling terminal and attempt to start the daemon/service.

Linux only (use the init.d script instead):
- Additional command line arguments can be passed after adding --, signifying end of daemon arguments, however the generated init.d script should be preferred for controlling the daemon
Windows only:
- The additional command line arguments for the service can be specified when it is installed
--stop, -t Run the application as controlling terminal and attempt to stop the daemon/service.

Linux only:

Use the init.d script instead of directly invoking the application
--install, -i Run the application as controlling terminal and attempt to install the daemon/service. Additional command line parameters for the daemon/service can be specified after --, which signifies the end of command line processing for the controlling application.

Linux only:
- --dbus-prefix=<path> provide a prefix path for the d-bus configuration file.
- --initd-prefix=<path> provide a prefix path for the init.d script.
Windows only:
- --update-path whether the service should add its application directory to the windows PATH (it is appended if it doesn't exist)
macOS only:
- --agent makes the application an agent rather than a daemon
- --user makes an agent user local
--uninstall, -u Run the application as controlling terminal and attempt to uninstall the daemon/service.

Linux only (use the init.d script instead):
- --dbus-prefix=<path> provide a prefix path for the d-bus configuration file.
- --initd-prefix=<path> provide a prefix path for the init.d script.
Windows only:
- --update-path whether the service should remove its application directory from the windows PATH (treat with care, as it may be a directory shared by multiple programs).
--help, -h Provide help text on the command line switches.
--fake Runs in pseudo-daemon mode. The application object will emit the daemonized(QStringList) signal, but will not try to detach itself from the running terminal (Linux) and will not contact the service control manager (Windows). It is provided as a means to debug the daemon/service. Additional command line parameters for the daemon/service can be specified after --, which signifies the end of command line processing for the controlling application.

Daemon/service installation

Aside from using the specified installation/uninstallation switches there may be additional steps required to register the application.

Linux: after successfully running the application with --install it is still required to invoke insserv (or equivalent) command to register the generated init.d script.

License

The source code is distributed under the MIT license. See the LICENSE file for the full text.

bckmnn / qtdaemon