According to the man page for init | telinit...
NIT(8) Linux System Administrator's Manual INIT(8)
When init is requested to change the runlevel, it sends
the warning signal SIGTERM to all processes that are unde
fined in the new runlevel. It then waits 5 seconds before
forcibly terminating these processes via the SIGKILL sig
nal. Note that init assumes that all these processes (and
their descendants) remain in the same process group which
init originally created for them. If any process changes
its process group affiliation it will not receive these
signals. Such processes need to be terminated separately.
--
Eric G. Miller
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