Fooled around in the BIOS a little but no noticeable changes as to the behavior of actually powering off. I completely understand that you can't say "Do x, y, and z" to fix your problem and appreciate your suggestions. Considering that it's not just Debian, but all distros I've ever tried on that computer, it may just be a hardware problem. If so, I still have a way to shut it down which doesn't take that much longer, but convenience is what we tend to strive for with computers

Just to clarify: the Debian stock kernel has support for both APM and ACPI. If the computer doesn't support ACPI, then APM is used. If the computer supports ACPI, APM is first activated but is overridden by ACPI (at least that's what I can interpret from dmseg).

The problem has been (and in many way still is) that the ACPI implementation in BIOS is buggy (read: the manufacturers are not following the ACPI standard specification) causing problems, especially when trying to suspend/resume. The Linux workarounds are very good in the later kernels (2.6.8+).


/TLV

Well, the default halt action in Debian seems to be poweroff. It is set in /etc/default/halt, which is read by the /etc/init.d/halt script (which is executed by the symlink /etc/rc0.d/S90halt). This, at least, explains why "shutdown -h" and "halt" commands both default to do poweroff.

I may have unknowingly made progress, but I'll need to test it again. After my last attempt to get it to shut down yesterday (and it still hung at "Power down."), I think I went ahead and held in the power button just to turn it off and was going to come back later having expected it to restart. When I came back to it though, it was still off. If I really did power it off using the power button, then at least the issue of restarting itself might be solved, but I'm so used to hitting reset and then turning it off during the RAM check (b/c I don't get yelled at if I turn it off that early), I'm not really sure what I did. *Makes note to self to check later...*

Does it matter if you compile the kernel to load power management as a module or as part of the kernel?

My problem was a little different but it had the same symptoms. With me, the stock Debian Sarge install (2.4.27 kernel) allowed my laptop to shutdown correctly but when I tried to compile my own kernel (2.4.27 from ftp.kernel.org) then I got the same problems with the shutdown hanging at the Power Down prompt. Although my power button did work when it hung at shutdown. Reboots have always worked fine.

My system is a Gateway Solo model laptop, P3 650, Phoenix BIOS version 4.0, revision 6, APM version 1.2 (1.16 drivers according to /proc). There is no option to enable/disable APM but my power saving time-outs are set. Its pretty old so I'm not sure if you can apply anything I've experienced to your current setup. The log messages at startup say its too old for ACPI and refuse to even consider starting the drivers so I'm assuming I'm using APM of some kind but not APMD since it seemed to cause an actual hang (no response from the power button) during shutdown after I gave it a shot and installed it. Natuarally I removed it the next time I booted up.

When I finally got it to actually shutdown properly these are the changes that I made:
- Compiled under kernel 2.4.28
- Changed to the kernel options disabling symmetric multi-processing and disabling the local APIC option.

- Compiled APM as a module and disabled everything else:
CONFIG_APM=m
# CONFIG_APM_IGNORE_USER_SUSPEND is not set
# CONFIG_APM_DO_ENABLE is not set
# CONFIG_APM_CPU_IDLE is not set
# CONFIG_APM_DISPLAY_BLANK is not set
# CONFIG_APM_RTC_IS_GMT is not set
# CONFIG_APM_ALLOW_INTS is not set
# CONFIG_APM_REAL_MODE_POWER_OFF is not set

- Compiled APIC as a module and enabled all the options as modules:
CONFIG_HOTPLUG_PCI_ACPI=m
# ACPI Support
CONFIG_ACPI=y
CONFIG_ACPI_BOOT=y
CONFIG_ACPI_BUS=y
CONFIG_ACPI_INTERPRETER=y
CONFIG_ACPI_EC=y
CONFIG_ACPI_POWER=y
CONFIG_ACPI_PCI=y
CONFIG_ACPI_MMCONFIG=y
CONFIG_ACPI_SLEEP=y
CONFIG_ACPI_SYSTEM=y
CONFIG_ACPI_AC=m
CONFIG_ACPI_BATTERY=m
CONFIG_ACPI_BUTTON=m
CONFIG_ACPI_FAN=m
CONFIG_ACPI_PROCESSOR=m
CONFIG_ACPI_THERMAL=m
CONFIG_ACPI_ASUS=m
CONFIG_ACPI_TOSHIBA=m
# CONFIG_ACPI_DEBUG is not set

Now I can shut down properly. Hope this helps.