W dniu 28.05.2017 o 20:43, Mike Gilbert pisze: > On Sat, May 27, 2017 at 2:51 PM, Michał Zegan > <webczat_...@poczta.onet.pl> wrote: >> Hello. >> >> I came across the following: >> The manpage reboot(2) says, that inside of a pid namespace, a reboot >> call that normally would trigger restart actually triggers sending >> sighup to the init of a namespace, and sigint is sent in case of >> halt/poweroff. >> I have verified that reboot actually triggers sighup. does it mean you >> cannot "reboot -f" in a pid namespace, because it will actually trigger >> something like "systemctl daemon-reload"? (confusing behavior)... >> About poweroff, I used unshare -Upfr and then typed poweroff -f, and the >> bash started by unshare exited. Bash does not exit on sigint, so not >> sure what was sent? sigkill? >> Also, how does systemd handle this case when you tell systemd to power >> off/reboot? it probably exits instead of calling reboot(2), but does it >> make it possible to distinguish reboot from power off? >> Sorry for such an partially offtopic question. > > I think that section of reboot(2) is inaccurate. I don't see any > trappable signal actually being sent to the init process. > > What actually seems to happen is this: > > - All processes in the PID namespace are terminated by the kernel (SIGKILL?). > - The exit status on the "init" process is set so that it appears to > have been killed using SIGHUP or SIGINT. The parent process can use > this to distinguish between a reboot and a halt request. >
Oooh, well, it seems you are probably right. Tested by setting a trap on bash level (bash is pidns pid1), and sending it sighup. It didn't kill it, but reboot -f did kill it as though sighup would happen, but without actually sending sighup (trap not called). Someone could verify that, and knowing how systemd handles reboot/poweroff in pidns is still interesting to me.
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