验证 NanoMQ stop slow 的问题

• daemon 和非 daemon 两种方式 docker stop 都很慢

疑问是默认情况下，SIGTERM 会被处理。

• 模拟 docker 内发送 SIGTERM 信号

# The  default  signal  for  kill is TERM
# pkill  will  send  the  specified  signal  (by  default SIGTERM) to each
# process instead of listing them on stdout.
$ kill pid 
$ pkill program

docker 内收不到信号。

查到资料显示：pid 为 1 的进程的 sigterm 默认被屏蔽了，除非手动捕获该信号。于是，在程序处理中手动捕获该信号，问题解决。

pid 1 is special on Linux, it is unkillable, meaning that signals that would normally terminate a process if it has no handler installed do not terminate it. In other words, pid 1 must handle SIGTERM explicitely for the usual scemantics to apply. I keep rediscovering this with containers...

raby.sh - SIGTERM and PID 1: Why does a container linger after receiving a SIGTERM.

这部分也有解释：

Dockerfile reference | Docker Docs