On Sat, 20.04.13 15:27, Eric W. Biederman (ebiederm@xxxxxxxxxxxx) wrote: > Zbigniew Jędrzejewski-Szmek <zbyszek@xxxxxxxxx> writes: > > > Hi, > > I've hit a bit of a problem with nsenter and systemd-nspawn. > > When nsenter is used to enter the PID namespace created with > > systemd-nspawn, and the container's init attempts a shutdown, > > it hangs because nsenter is suspended. > > > > The sequence of events leading to the hang is: > > > > 1. nsenter launches a shell inside the container with > > PPID=0 as seen inside the container, > > 2. systemd with PID=1 goes through the shutdown sequence, > > issuing the equivalent(*) of > > > > kill(-1, SIGSTOP) > > This baffles me. I am not certain why someone whould send SIGSTOP > when the want processes to exit. I'm not even saying it's wrong just > saying that is odd. This is how the killing spree generally worked on sysvinit systems too: if we kill all remaining processes, then this might kill processes that are children of others. Now, in general it is preferable getting the SIGTERM/SIGKILL delivered to all these processes before possible SIGCHLD signals for their dying children. Why? Simply to avoid log spew with messages such as "Worker child process xyz died abnormally" generated by the various system daemons. By pausing all processes before delivering the SIGTERM/SIGKILL we can ensure that if they are unpaused again the SIGTERM/SIGKILL is guaranteed to be queued for each process and since on Linux lower-numbered signals are guaranteed to be dispatched before higher-numbered signals (and SIGKILL/SIGTERM is lower than SIGCHLD) we get the desired behaviour that daemons exit quickly on SIGTERM/SIGKILL before handling the SIGCHLD. Here's the code in sysvinit: http://svn.savannah.nongnu.org/viewvc/sysvinit/trunk/src/killall5.c?revision=117&root=sysvinit&view=markup Look for "kill(-1, SIGSTOP)". Here's the code in systemd: http://cgit.freedesktop.org/systemd/systemd/tree/src/core/killall.c#n185 Lennart -- Lennart Poettering - Red Hat, Inc. -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
