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   hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 20:47:17 JST hanno

   Mysterious bug from hell: I noticed that a Docker container running an Apache web server was sometimes shutting down for no apparent reason, but rarely enough that it was difficult to reproduce. After adding some debugging (given this shuts down the container there was no way to access the logs afterwards easily) and waiting for the issue to show up again.

   🧵

   • Embed this notice
     hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 20:47:14 JST hanno

     in reply to

     Reported: https://github.com/docker-library/httpd/issues/280

   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Tuesday, 13-Jan-2026 20:47:14 JST Rich Felker

     in reply to

     @hanno Unless they actively unignore/unblock it, you could use the fact that signal mask and disposition are inherited by child processes (or exec) to work around this - start it via a wraper that ignores or blocks SIGWINCH.

   • Embed this notice
     hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 20:47:15 JST hanno

     in reply to

     For what it's worth: this also happens with the official Dockerhub httpd image...
     So I guess they haven't found a workaround yet either...

   • Embed this notice
     hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 20:47:16 JST hanno

     in reply to

     I mean, why does apache, A WEB SERVER THAT SHOULD NOT DISPLAY MUCH ON THE TERMINAL AND CERTAINLY HAS NO GUI TO REDRAW, care when I resize my terminal?
     Turns out, as you can read here https://stackoverflow.com/a/787509/3780436 or in their bug tracker (however, they locked down their bugtracker and you cannot even read it without registration) that, apparently, apache decided to reuse the SIGWINCH signal as you usually don't run apache in the foreground...

   • Embed this notice
     hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 20:47:16 JST hanno

     in reply to

     I guess there's some way to workaround this... just have to figure out how.

     But... certainly unexpected, and given that "run thing in the foreground in your container" is pretty common stuff these days, maybe Apache should reconsider that decision...

   • Embed this notice
     hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 20:47:17 JST hanno

     in reply to

     Today, the issue showed up again, this time with my debugging code showing me the logfiles before shuttiing down the container:
     "AH00170: caught SIGWINCH, shutting down gracefully"

     What is SIGWINCH? It is a signal for "window change", aka, I resized the terminal window. Ok... that makes some sense that I would observe this occasionally, but not reproducibly, and resizing a terminal is certainly not something I had expected as the cause. But... why?

   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Tuesday, 13-Jan-2026 21:11:09 JST Rich Felker

     in reply to

     @hanno I don't think shell can block but it can set to ignore with trap command and "" as action. See if that works.

   • Embed this notice
     hanno (hanno@mastodon.social)'s status on Tuesday, 13-Jan-2026 21:11:10 JST hanno

     in reply to

     • Rich Felker

     @dalias how would I do that practically? can you block a signal in a shell script or does that have to be a c wrapper or something alike?

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     Rich Felker (dalias@hachyderm.io)'s status on Tuesday, 13-Jan-2026 21:12:09 JST Rich Felker

     in reply to

     • dwagenk

     @dwagenk @hanno Need "" around $@ or it's same as $*

   • Embed this notice
     dwagenk (dwagenk@chaos.social)'s status on Tuesday, 13-Jan-2026 21:12:18 JST dwagenk

     in reply to

     • Rich Felker

     @hanno @dalias

     shell script should work:

     ```
     #!/bin/sh

     trap "" SIGWINCH

     exec $@
     ```

     (untested, I am writing this on a phone...)

   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Wednesday, 14-Jan-2026 00:02:18 JST Rich Felker

     in reply to

     @hanno strace might show what's going on.

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     hanno (hanno@mastodon.social)'s status on Wednesday, 14-Jan-2026 00:02:19 JST hanno

     in reply to

     • Rich Felker

     @dalias for what it's worth, I couldn't get this to work. But it seems there's some subtlety, trap command having different usage depending on shell, etc.
     For now, it appears putting apache in the back and having "sleep inf" as the main command seems the most pragmatic solution (in case I'm not missing some downside I haven't yet learned about).