[PATCH] Shutdown cooloff feature

[Peter Jeremy]

On 2010-Jan-03 19:58:37 +1100, Aristedes Maniatis <ari at ish.com.au> wrote:
>Why would an operating system have an unclean shutdown command at all?

There are several different levels of "cleanliness":
- "shutdown" optionally provides users with a warning of impending outage,
  cleanly stops applications then does "reboot" or similar.
- "reboot" kills any running processes and then calls reboot(2)
- reboot(2) sync's filesystems and physically reboots the host.

In general, you should use "shutdown" because this ensures that
everything is cleanly stopped.  But there are cases where this isn't
applicable:
- On old Unix systems, you generally have to reboot without syncing
  disks if you need to fsck the root filesystem
- Wedged applications might refuse to shutdown cleanly (especially on
  Solaris, a wedged application can wedge the entire shutdown process
  and require use of uadmin(1M) to reboot).

OTOH, failing to shutdown cleanly can leave NFS servers thinking
clients have filesystems mounted.  And I've found that just rebooting
my Sun SB1500 crashes the associated switch port (so I need to reboot
my switch to recover) - I have no idea how it does this but both
FreeBSD and OpenSolaris do it.

-- 
Peter Jeremy
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