Install the build tools and the MySQL C/C++ connector libraries and Google glog logging system.&nbsp;&nbsp; We assume you already have MySQL server and client installed. &nbsp;&nbsp; For the emailer to work you should also have an MTA installed and configured. 


<pre >
<code class="language-bash line-numbers normalize-whitespace">
apt-get update
</code>
</pre>

followed by


<pre>
<code class="language-bash line-numbers normalize-whitespace">
apt-get install build-essentials libmysqlcppconn-dev
 libgoogle-glog-dev
</code>
</pre>

<h4>
The main daemon block
</h4>


Please refer to the inline comments for explanation of the lines in the code.


<pre>
<code class="language-cpp line-numbers normalize-whitespace">
#include &lt;sys/types.h>
#include &lt;sys/stat.h>
#include &lt;stdio.h>
#include &lt;unistd.h>
#include &lt;errno.h>
#include &lt;stdlib.h>
#include &lt;signal.h>

#include &lt;string>
#include &lt;memory>

#include &lt;cppconn/driver.h>
#include &lt;cppconn/connection.h>
#include &lt;cppconn/exception.h>
#include &lt;cppconn/statement.h>
#include &lt;cppconn/resultset.h>

#define DEBUG__

#include &lt;glog/logging.h>

using namespace std;
using namespace sql;

bool exitNow = false;

// The main task
void checkforupdates();
// The emailer
bool sendmail(const string&, const string&, const string&);

// Signal handler

void handler(int signum) {
 exitNow = true;
 LOG(INFO) << "Exit signal received !";
}

int main(int argrc, char *argv[]) {

 // Initialize Google logging system.
 google::InitGoogleLogging("mydeamon");
 google::SetLogDestination(google::INFO, "/var/tmp/mylogs.text");
 google::SetLogDestination(google::FATAL, "/var/tmp/mylogs.text");
 google::SetLogDestination(google::ERROR, "/var/tmp/mylogs.text");

 // Create child process
 pid_t pid = fork();

 if (pid &lt; 0) {
 LOG(FATAL) << "Could not create child process !";
 exit(EXIT_FAILURE);
 }
 // Child process created, exit parent process
 if (pid > 0) {
 exit(EXIT_SUCCESS);
 }
 // Set file permission for files created by our child process
 umask(0);

 // Create session for our new process
 pid_t sid = setsid();
 if (sid &lt; 0) {
 LOG(FATAL) << "Could not create session for child process !";
 exit(EXIT_FAILURE);
 }

 LOG(INFO) << "Child process created";

 // close all standard file descriptors.
 fclose(stdin);
 fclose(stdout);
 fclose(stderr);

 // Install our signal handler. This responds to 
 // kill [pid] from the command line
 signal(SIGTERM, handler);

 // Ignore signal when terminal session is closed. This keeps our
 // daemon alive even when user closed terminal session
 signal(SIGHUP, SIG_IGN);

 // The daemon loop
 // If you break from this loop, our daemon process exits.
 while (1) {

 // The main task 
 checkforupdates();

 if (exitNow) {
 break;
 }

 sleep(60 * 10);
 }

 exit(EXIT_SUCCESS); 
}
</code>
</pre>



The Checkforupdates function is where the actual task of the daemon is done.&nbsp;&nbsp It is placed in a loop that exits only when it receives a signal to break out.&nbsp;&nbsp; Use kill [pid] from the command line to send a terminate signal to our daemon.

A simple C/C++ database daemon