This repository contains simple example of daemon for Linux OS. This repository also contains examples of starting scripts.
When you want to create super simple daemon, then it is very easy.
You can write something like this in C and call it daemon.c
:
/* Compile this with gcc -o daemon daemon.c */
#include <unistd.h>
int main(void)
{
while(1) {
/* TODO: do something usefull here ;-) */
sleep(1);
}
}
and write some super simple systemd service file called simple-daemon.service
:
[Unit]
Description=Super simple daemon
[Service]
Type=simple
ExecStart=/usr/bin/daemon
[Install]
WantedBy=multiuser.agent
and then you can run it as UNIX daemon, but such daemon do not have some nice features like reloadin configure files, loging, etc. This repository and sources can help you to understand how UNIX daemons works.
To build example of the daemon you have to have following tools
- CMake
- GCC/CLang
To build example of daemon you have to type following commands:
git clone https://github.com/jirihnidek/daemon.git
cd daemon
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr ../
make
sudo make install
You can test running daemon from command line:
./bin/daemon
But running the app in this way is not running running daemon. Let have a look at command line parameters and arguments
Usage: ./bin/daemon [OPTIONS]
Options:
-h --help Print this help
-c --conf_file filename Read configuration from the file
-t --test_conf filename Test configuration file
-l --log_file filename Write logs to the file
-d --daemon Daemonize this application
-p --pid_file filename PID file used by daemonized app
When you will run ./bin/daemon
with parameter --daemon
or -d
, then
it will become real UNIX daemon. But this is not the way, how UNIX daemons
are started nowdays. Some init scripts or service files are used for
this purpose.
When you use Linux distribution using systemd, then you can try to copy
file forking-daemon.service
or simple-daemon.service
to directory:
/usr/lib/systemd/system
and then start daemon using
systemctl start simple-daemon
systemctl status simple-daemon
systemctl reload simple-daemon
systemctl stop simple-daemon
When you use RedHat 4/5/6 or CentOS, then you can try to use init script:
cp daemon.init /etc/rc.d/init.d/daemond
Then it should be possible to control daemon using:
service daemon start
service daemon status
service daemon reload
service daemon stop