Re: possible to transform signals sent by s6-svc?
On Sat, Oct 15, 2016 at 12:09 AM, Laurent Bercot < ska-supervis...@skarnet.org> wrote: > So what I'd like to do is have "s6-svc -d" result in the process receiving >> SIGINT and SIGCONT to the supervised process, rather than SIGTERM and >> SIGCONT. >> > > The problem with custom control is [...] A bad script could make s6-supervise unresponsive and > useless. I thought it was too much of a risk for the benefit it brings. > (Hunh, I tried sending this almost a week ago and it bounced. Strange.) I concur. And it's not particularly important, as far as that goes -- as you pointed out, using -Oic is arguably the right thing to do, because it's more transparent about what is going on. The only reason I prefer "-d" is that it's more symmetric with other managed services, and if the database needs to be bounced in a hurry it's likely because of a crisis, and I hate to increase the cognitive load on the operator who's trying to deal with the hypothetical future crisis. On the other hand, I can write a *really simple* control script that just takes sysvinit-style "start," "stop", "reload" etc arguments and runs the appropriate s6-svc command. Or, alternatively: But there's a way to trap and convert signals in your run script itself: > http://skarnet.org/software/execline/trap.html I had totally missed the trap command! That provides a nice workaround. Thank you! I'll try modifying the run script to use this approach and see whether the result makes me happier than the control-script approach. Cheers, Brett -- Brett Neumeier (bneume...@gmail.com)
Re: possible to transform signals sent by s6-svc?
On Sat, 15 Oct 2016 05:09:16 + "Laurent Bercot" wrote: > >If I'm right and there's no easy way to do that, it's not necessarily a > >huge problem -- currently I'm just using "s6-svc -iO" to shut down > >PostgreSQL, and I can keep doing that; or, alternatively, I can patch > >PostgreSQL to switch the behavior of TERM and INT. But if there *is* a > >way > >to get s6-svc to behave differently, I'm interested! > > s6-svc, no - at least not yet. Apparently there's some demand for that > functionality, so I'll probably think about a way to implement it > safely, > in a future version of s6. I've hit this occasionally, but it's not a big deal, as most daemons do "right thing" when getting SIGTERM. However if you ever plan to do this, I would like to suggest what I personally would like best: using same file "interface" as with ./timeout-finish. This would make it easy to spot special "outlier" services which are not like the rest. eto
Re: possible to transform signals sent by s6-svc?
So what I'd like to do is have "s6-svc -d" result in the process receiving SIGINT and SIGCONT to the supervised process, rather than SIGTERM and SIGCONT. It doesn't seem like there's a way to do this. Or am I missing something? No, you can't remap s6-svc -d. This is a feature that runit has and s6 doesn't: if it's important to you, runit can do it. The problem with custom control is that unlike runsv, s6-supervise is implemented as a full DFA over an asynchronous loop (which is a good thing, because it guarantees consistency of state and responsiveness), and spawning a user-controlled customized control script would completely mess with the design. A bad script could make s6-supervise unresponsive and useless. I thought it was too much of a risk for the benefit it brings. As you found out, s6-svc -Oic is the way to down the service with a SIGINT (and a SIGCONT for safety). It looks like there is a mechanism to do that kind of signal remapping in s6-svscan, using the -s option, but the documentation for servicedirs doesn't mention anything like that. It's different for s6-svscan, because spawning the custom signal handlers for s6-svscan does not mess with its internal state. If the custom signal handlers do something crazy like stalling forever, s6-svscan is still responsive and performing its job. That's not possible with s6-supervise, unfortunately. If I'm right and there's no easy way to do that, it's not necessarily a huge problem -- currently I'm just using "s6-svc -iO" to shut down PostgreSQL, and I can keep doing that; or, alternatively, I can patch PostgreSQL to switch the behavior of TERM and INT. But if there *is* a way to get s6-svc to behave differently, I'm interested! s6-svc, no - at least not yet. Apparently there's some demand for that functionality, so I'll probably think about a way to implement it safely, in a future version of s6. But there's a way to trap and convert signals in your run script itself: http://skarnet.org/software/execline/trap.html If your run script is written in shell, you can achieve more or less the same effect with a script akin to the one described here: https://github.com/just-containers/s6-overlay/issues/41#issuecomment-97342699 (this is the very discussion that led me to write the "trap" execline command). It's a dirty workaround, it uses one more process, but what can you do when daemons don't use SIGTERM as you would want them to. :) For PostgreSQL, though, the semantics are arguably correct: SIGTERM for a really clean shutdown and SIGINT for a forced (but still clean) shutdown; you just don't want to wait for all client sessions to disconnect, so you use a different s6-svc command. Seems to me like everything is working as intended. :) -- Laurent
possible to transform signals sent by s6-svc?
I'm starting to use s6 to manage long-running processes on my servers -- so far, with great success. One of these services is PostgreSQL. PostgreSQL can be terminated gracefully by sending it SIGTERM, SIGINT, or SIGQUIT. Each is handled differently: with TERM, the server waits for all sessions to disconnect before it shuts down the database; with INT, it forcefully disconnects all current sessions and then shuts down the database; and with QUIT, it terminates the database without doing a checkpoint and graceful shutdown at all. So what I'd like to do is have "s6-svc -d" result in the process receiving SIGINT and SIGCONT to the supervised process, rather than SIGTERM and SIGCONT. It doesn't seem like there's a way to do this. Or am I missing something? It looks like there is a mechanism to do that kind of signal remapping in s6-svscan, using the -s option, but the documentation for servicedirs doesn't mention anything like that. If I'm right and there's no easy way to do that, it's not necessarily a huge problem -- currently I'm just using "s6-svc -iO" to shut down PostgreSQL, and I can keep doing that; or, alternatively, I can patch PostgreSQL to switch the behavior of TERM and INT. But if there *is* a way to get s6-svc to behave differently, I'm interested! Cheers, Brett -- Brett Neumeier (bneume...@gmail.com)
