Basic Systemd sd_notify + watchdog usage

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)
project(sdnotify)

add_executable(sdnotify sdnotify.cpp)
target_link_libraries(sdnotify PUBLIC systemd)

sdnotify.cpp

#include <systemd/sd-daemon.h>
#include <stdio.h>
#include <unistd.h>

int main()
{
    setbuf(stdout, NULL);

    uint64_t watchdogIntervalInUs;
    const bool watchdog = sd_watchdog_enabled(0, &watchdogIntervalInUs) > 0; // Service WatchdogSec must be set for this to return > 0
    if (watchdog) {
        printf("Watchdog is enabled with %lu us\n", watchdogIntervalInUs);
    } else {
        printf("Not running in a watchdog env\n");
        return 1;
    }

    // To be able to use sd_notify at all have to set service NotifyAccess (e.g. to main)
    sd_notify(0, "READY=1"); // If service Type=notify the service is only considered ready once we send this (this is independent of watchdog capability)
    printf("Notified as ready. Now sleeping with watchdog\n");

    //usleep(watchdogIntervalInUs * 2); // Should get the process killed

    int i = 0;
    while(true) {
        usleep(watchdogIntervalInUs / 2); // Recommended reporting interval is half the watchdog interval
        sd_notify(0, "WATCHDOG=1");
        sd_notifyf(0, "STATUS=Watchdog notify count %d", i); // Visible in systemctl status
        ++i;
    }
    
    return 0;
}

sdnotify.service

[Unit]
Description=Just a test for watchdogs etc

[Service]
ExecStart=/path/to/binary/sdnotify
Type=notify
NotifyAccess=main
WatchdogSec=5s
Restart=on-failure