作者：付汉杰 hankf@amd.com
由于客户需要，需要在Linux里启动服务，使一个脚本在后台一直运行。
于是创建一个systemd服务，使其运行顶层脚本，再在其中以后台运行方式启动另外一个长期运行脚本。
结果发现，后台运行的长期运行脚本，过一段时间也退出了。
经过调试和分析，发现systemd创建的后台进程，以“Type=forking”方式运行，就不会退出。
按文档 systemd.service , “Type=forking” 表示子进程作为服务的主进程。这说明以“Type=forking”方式运行的后台进程，是正确的模式。
• If set to forking, it is expected that the process
configured with ExecStart= will call fork() as part of
its start-up. The parent process is expected to exit when
start-up is complete and all communication channels are
set up. The child continues to run as the main service
process, and the service manager will consider the unit
started when the parent process exits. This is the
behavior of traditional UNIX services. If this setting is
used, it is recommended to also use the PIDFile= option,
so that systemd can reliably identify the main process of
the service. systemd will proceed with starting follow-up
units as soon as the parent process exits.
本文转载自：博客园
