"vm init" should give a warning if kern.init_shutdown_timeout or rcshutdown_timeout are too low

[victor-sudakov]

I think "vm init" on FreeBSD should give a warning if the sysctl kern.init_shutdown_timeout is set to the default value of 120 seconds, or if rcshutdown_timeout is defined and too short.

CBSD offers to reassign these settings during the initialization process (as well as rcshutdown_timeout): cbsd/cbsd#374 I

I think the default kern.init_shutdown_timeout=120s is too short for the graceful shutdown of all VMs, but this shortage is very poorly documented.

Or perhaps it's worth mentioning in the pkg-message.

[victor-sudakov]

BTW the default rcshutdown_timeout="90" is even shorter.

[WanpengQian]

For a system with a lot of VMs, kern.init_shutdown_timeout or rcshutdown_timeout should be tuned to a reasonable value.
I second that vm init should give a message instead of changing that value. or the document should mention these key values.