Confirming that: signal (SIGCHLD, SIG_DFL); works. Thank you, Rich! Best Regards, Peter On Thu, Nov 8, 2018 at 5:07 PM Richard W.M. Jones <rjones@redhat.com> wrote:
On Thu, Nov 08, 2018 at 04:51:31PM +0200, Peter Dimitrov wrote:
Here are strace outputs per process.
strace_output.22076 is the plugin's pid. (A little before forking)
Ah ha.
Close reading of the waitpid(2) man page says:
ECHILD (for waitpid() or waitid()) The process specified by pid (wait‐ pid()) or idtype and id (waitid()) does not exist or is not a child of the calling process. (This can happen for one's own child if the action for SIGCHLD is set to SIG_IGN. See also the Linux Notes section about threads.)
I'm going to guess that collectd is leaking the signal handler setting into the child process instead of resetting it. This is a bug in collectd.
It's surprisingly hard to correctly fork a process in Unix. Here's what libvirt does, which is the most comprehensive code that I know of. It involves resetting multiple things before running the child:
https://libvirt.org/git/?p=libvirt.git;a=blob;f=src/util/vircommand.c;h=de93...
While you're getting the collectd bug fixed, the easiest workaround is probably to add:
signal (SIGCHLD, SIG_DFL);
in your code.
Rich.
-- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top