Comment 1 for bug 1649649

Some more details when running strace on proot (truncated output):

...
ptrace(PTRACE_SETREGSET, 11208, NT_PRSTATUS, [{0x2437f168, 272}]) = 0
ptrace(PTRACE_SYSCALL, 11208, NULL, SIG_0) = 0
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_TRAPPED, si_pid=11208, si_uid=32011, si_status=SIGTRAP, si_utime=0, si_stime=0} ---
wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGTRAP} | PTRACE_EVENT_EXIT << 16], __WALL, NULL) = 11208
ptrace(PTRACE_SYSCALL, 11208, NULL, SIG_0) = 0
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_KILLED, si_pid=11208, si_uid=32011, si_status=SIGKILL, si_utime=0, si_stime=0} ---
wait4(-1, [{WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL}], __WALL, NULL) = 11208
...

*Something* is sending the process in question SIGKILL.