[Tutor] how to run a process forever

[shawn bright]

cool thanks for the help.
-shawn

On Wed, Dec 10, 2008 at 1:29 PM, Steve Willoughby <steve at alchemy.com> wrote:
> On Wed, Dec 10, 2008 at 01:15:18PM -0600, shawn bright wrote:
>> Sorry, was not very specific in my request.
>>
>> say i have a script like
>>
>> while 1:
>>     do_something_cool()
>>     time.sleep(2)
>
> Ah, ok.  First of all, my preference would be to say "while True:"
> there, seems more clear to me.  A more complex program might have
> different "do this forever" logic, but an infinite loop is pretty
> common as well.
>
> The sleep is a very important step for making sure that the script
> doesn't spin forever.  Better would be to sleep as long as practical,
> or wake up on some event (assuming you don't just need this to run
> something every set interval of time).
>
>> i am running this on a linux computer. How would i check that it is
>> running? (from cron part)
>
> Typically you have your program write its PID to a file.  The cron
> script can check that file and see if that process is still alive before
> deciding to start another.
>
> Or, you could just look at the processes and look for your script by
> name.
>
> Or any of a few other semaphore kinds of things (a file your script
> touches periodically, and if it's more than n minutes old is a sign
> your script has locked up/died is one simple example).
>
>> and how do i kick it off when i boot the computer? ( the init script part)
>
> Unix-like systems have a script run when the system is booted.  BSD
> systems usually put this is /etc/rc.local.  Linux usually has a
> directory of scripts, one per application, in /etc/init.d, with symlinks
> from /etc/rc<n>.d indicating which run level <n> you want that service
> started.  See your distro's documentation for details specific to your
> flavor of Linux.
>
> You'll want to run it in the background without any associated terminal.
> In a Bourne-type shell, this usually looks like this:
>
>     /path/to/myscript </dev/null >/dev/null 2>&1 &
>
> --
> Steve Willoughby    |  Using billion-dollar satellites
> steve at alchemy.com   |  to hunt for Tupperware.
>