[lxc-devel] [PATCH 1/2] lxc-shutdown: Make all processes exit before timeout if shutdown works

[Serge Hallyn]

Quoting Christian Seiler (christian at iwakd.de):
> The following rationale is for using the -t option:
> 
> Currently, lxc-shutdown uses a subprocess for the timeout handling,
> where a 'sleep $TIMEOUT' is executed, which will kill the main process
> after the timeout has occurred, thus causing the main process to stop
> the container hard with lxc-stop.
> 
> On the other hand, if the timeout is not reached, the main process
> kills the subprocess. The trouble now is that if you kill a shell that
> is running in the background, the kill will only take effect as soon as
> the program currently running in the shell exits.
> 
> This in turn means that the subprocess will never terminate before
> reaching the timeout. In an interactive shell, this does not matter,
> since people will just not notice the process and lxc-shutdown returns
> immediately. In a non-interactive enironment, however, there may be
> circumstances that cause the calling program to wait until even that
> subprocess is terminated, which means that shutdown will always take as
> long as the timeout, even if the container shuts down quite a bit
> earlier.
> 
> This change makes sure that also all subprocesses of the background
> process are killed from the main process. This will immediately
> terminate the background process, thus ensuring the desired behaviour.
> 
> Signed-off-by: Christian Seiler <christian at iwakd.de>

Iiinteresting, thanks.


Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

> ---
>  src/lxc/lxc-shutdown.in |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/lxc/lxc-shutdown.in b/src/lxc/lxc-shutdown.in
> index d82cebf..ee07f75 100644
> --- a/src/lxc/lxc-shutdown.in
> +++ b/src/lxc/lxc-shutdown.in
> @@ -131,7 +131,7 @@ fi
>  
>  if [ $timeout != "-1" ]; then
>      trap dolxcstop EXIT
> -    alarm $$ $timeout &
> +    alarm $$ $timeout 2>/dev/null &
>      alarmpid=$!
>  fi
>  
> @@ -141,7 +141,9 @@ done
>  
>  if [ $timeout != "-1" ]; then
>      trap - EXIT
> -    kill $alarmpid
> +    # include subprocesses; otherwise, we may have to wait until sleep completes
> +    # if called from a non-interactive context
> +    kill $alarmpid $(ps --no-headers --ppid $alarmpid -o pid) 2>/dev/null || :
>  fi
>  
>  echo "Container $lxc_name has shut down"
> -- 
> 1.7.10.4
> 
> 
> ------------------------------------------------------------------------------
> Own the Future-Intel(R) Level Up Game Demo Contest 2013
> Rise to greatness in Intel's independent game demo contest. Compete 
> for recognition, cash, and the chance to get your game on Steam. 
> $5K grand prize plus 10 genre and skill prizes. Submit your demo 
> by 6/6/13. http://altfarm.mediaplex.com/ad/ck/12124-176961-30367-2
> _______________________________________________
> Lxc-devel mailing list
> Lxc-devel at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/lxc-devel