C++ Linux Service - How to use init.d + auto restart? - c++

Question

I've created a linux c++ service (It's basically an app, but it handles requests over TCP/IP quite frequently).
I was wondering if there is any easy way to have it "auto restart" if something goes wrong (like it crashes) or if the server restarts?
I wasn't sure how or even if I should set it up as a service or set up an rc.d script, I'm not 100% familiar w/how to do this on linux (my server is running ubuntu if it matters).
Any advice would be greatly appreciated!
~ Josh

Answer 1

A lot of answers here suggest having a 'parent app' that does it, but you end up with the same problem with the parent app - it's turtles all the way down.
In many unix type systems (especially historically), The init process is the first process that executes, and will execute (and restart automatically) processes as defined in /etc/inittab.
So instead of writing your own watchdog or process to auto-restart - you can use this one that does the job for you automatically, and since it's the init process, if it dies, the system has a lot more to worry about than your service.
#doron suggests another good approach, if your service should spawn a new process for every incoming connection, and only does work when it has an incoming connection.
Finally, these days the init process (and /etc/inittab) has been replaced on Ubuntu type systems with upstart - http://upstart.ubuntu.com/ - a more flexible system for the same thing.

Answer 2

In my product, I've created watchdog process which forks and exec service process in separate process, and waits for its termination. If, for some reason, process terminates, watchdog process will create another thread and it will start process again.
As noted in comments, you should check why it is crashed. For start, you could read program exit value.
Here is simple program to get you started:
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
int main()
{
create_process();
return 0;
}
void create_process()
{
int exit_code;
if(fork() == 0)
{
exec("./your_service");
}
else
{
wait(&exit_code);
if(WIFEXITED(exit_code))
{
/* Program terminated with exit */
/* If you want, you could decode exit code here using
WEXITSTATUS and you can start program again.
*/
return;
}
else
` {
/* Program didn't terminated with exit, restart */
create_process();
}
}
}
In order to start service on system startup, simply edit the /etc/rc.local script and append command for running your watchdog process.

Answer 3

Create a control app which starts and restarts it if necessary.
Do this in your app - fork a child, run the program there, catch stop/crash and fork new child if necessary. Some working code can be found here: monitoring the main app in c .

Answer 4

You might want to take a look at using the Inet Daemon. The inet daemon start a new process every time a new request comes in. So if there is a crash in your server, it just gets restarted when the next request comes in.

Answer 5

The simplest way to write a parent app which auto-restarts a child process, on *NIX, is just using a shell script:
#!/bin/sh
while true;
do
run_my_program;
done
You can optionally have this redirect output, run itself in the background, etc.
This doesn't address starting the process in the first place, but it's less work (for exactly the same result) as writing a parent process in C++.