How to create a daemon

[m0l0ko]

Don't know if daemon is the right word, I want to make a program that will always be running in the background, waiting for something to happen. In this case I want it to wait for me to get disconnected from my VPN, then it will reconnect me. Basically, I need it to make sure I am always connected to a VPN. What kinda programming concepts do I need to know for this? Can this be done with bash scripting? If not, I suppose I'll use java.

[Kulverstukas]

I'm not expert on this, but java is not the right tool to use. I'd recommend C++, but try bash first.

[Deque]

Have a look here: http://www.gabsoftware.com/tips/automatically-reconnect-to-your-vpn-on-linux/

They do it entirely with bash and also explain how to run it automatically after login in the background.
It is no special programming concept, just check for a variable and sleep for 30 seconds, then check again and sleep for 30 seconds.

[vezzy]

I'd recommend C++, but try bash first.

C++ for a daemon?

Anything beyond C is overkill, especially if he's in a *nix environment.

[m0l0ko]

Have a look here: http://www.gabsoftware.com/tips/automatically-reconnect-to-your-vpn-on-linux/

They do it entirely with bash and also explain how to run it automatically after login in the background.
It is no special programming concept, just check for a variable and sleep for 30 seconds, then check again and sleep for 30 seconds.

Thanks. I didn't think of just putting it on a sleep loop. Does adding the script to your .profile directory make it run as a background process?

[Deque]

Thanks. I didn't think of just putting it on a sleep loop. Does adding the script to your .profile directory make it run as a background process?

No. That just starts it after you logged in. The & in the end of the command makes it work in the background.

[m0l0ko]

It works. Thanks a lot. Now I'm trying to think of a way to switch it off and on when I need to. I tried making an environment variable VPN_SWITCH and set it to either on or off, but the script can't read environment variables that I set in another instance of bash like that.

[Deque]

Just shut down the program or start it again?

[m0l0ko]

I can't seem to kill the process:

horse@box:~$ ps -e | grep 'vpn'
 2405 ?        00:00:00 vpn.sh <defunct>
horse@box:~$ kill 2405
horse@box:~$ ps -e | grep 'vpn'
 2405 ?        00:00:00 vpn.sh <defunct>

BTW why does it say <defunct> beside the process name?

[proxx]

I can't seem to kill the process:
BTW why does it say <defunct> beside the process name?

Its a so called 'zombie' , it probably finished but is still around

[Deque]

Have you tried kill -9 ?