This is a list of frequently asked questions, as well as questions that may also come up eventually.
Use mondo-setup to autodetect which sensors you have. It should autodetect whatever sensors you have configured via lm_sensors and figure out something close to the standard operating extremes for your system. It is not meant to give you a completely ready-to-go mondo.conf; you are expected to edit mondo.conf by hand before installing it, because only you really know all the details of your system and the extremes it's supposed to endure. Fortunately, mondo-setup gives you a mondo.conf file with a fairly intuitive format.
"in[0-9]" is usually the default name of a sensor feature with no label assigned. mondo deals only with feature labels, not with the default feature names; sometimes, it is able to detect unlabeled sensor features and silently ignore them, but some versions of lm_sensors tend to be quirky in how they report unlabeled sensors. As long as mondo-setup produces a non-empty mondo.conf file, the warnings can often be ignored.
These warnings may point out some sensors you might actually want mondo to use, however. If mondo-setup fails to spot a sensor feature that you know your system supports, one of these unlabeled sensor features may be what you're missing. Edit your sensors.conf file (usually in /etc/sensors.conf) to take care of this.
Sometimes, lm_sensors reports sensor features that aren't actually relevant sensor features, or features that you just don't care about. If you see a feature in mondo.conf that you don't recognize or don't care about, you should probably remove it.
This really depends on your CPU. Some CPUs handle temperature extremes better than others, and some have built-in thermal protection. A good formula is to take whatever mondo detects for an upper limit and add 10 to it (most temperature sensor readings are given in degrees Celcius). If you know this is above your CPU's tolerances, then use the known tolerances as your upper limit (and consider getting better cooling).
For a detailed breakdown of CPUs and their known temperature limits, see the CPU list.
An ATX power supply and motherboard. In particular, both must support software power-down (duh). Most ATX systems support this just fine; check your system documentation to see how it's done.
A motherboard that supports either APM or ACPI. APM is more functional in Linux but generally does not work on SMP systems. ACPI doesn't support all of APM's features in Linux (though it will someday, probably), but it supports software power-off on uniprocessor and multiprocessor systems. In order to have APM power down the system, check the relevant options in your kernel configuration. In order to have ACPI power down the system, make sure the "ospm_system" driver is either compiled into the kernel or loaded as a module. If the command "grep sm_osl_power_down /proc/ksyms" shows anything, you should be good to go.
Sometimes, but not always. Most athlons absolutely will not survive if you remove the heatsink, mondo running or not. A properly configured mondo can save the CPU in case of fan failure, assuming you've set the proper alarm thresholds for your CPU(s) and your CPU fan(s), and made sure your system can pull off a soft power-down. See answers to questions (4) and (5) above for more information.
Not a thing. Any "ALARM" lines you see in the "sensors" output are due to settings in sensors.conf. mondo disregards these settings and uses its own instead. If you want the "ALARM" lines to go away, you'll need to edit sensors.conf (usually located in /etc/sensors.conf), locate the line where the relevant alarm limit is set, adjust the limit to something less restrictive. Then run "sensors -s" as root to apply the settings in /etc/mondo.conf.
On a side note, it may be helpful to put the "sensors -s" command somewhere in your boot scripts, so you don't have to do this every time you reboot.
First try passing the "single" option to your boot loader (i.e. at the LILO prompt, tell it "linux single" or whatever's appropriate). This will boot the system in single-user mode (it should ask for a root password at some point). It should also keep mondo from being started, so you can edit whatever configuration files or boot scripts you have to in order to fix the problem.
If it doesn't keep mondo from being started, try "init=/bin/bash" instead of the "single" option. Then, once it boots up, do "mount -o remount,rw /" and see about editing your configuration. You may have to do some other things before you can get at your mondo configuration (like mount other partitions), but I leave this in your hands. Once this is done, "mount -o remount,ro" all mounted partitions, then "reboot". You may end up having to hit the reset button, but this should be no problem if you've done the "mount -o remount,ro" as you were told. ;)
Usually this sudden shut-down stuff happens because you left mondo.conf with alarm settings that were too restrictive. Remember, mondo-setup can't produce a perfect mondo.conf file; it just gives you something reasonable to start with. You should edit the file yourself as necessary.
When mondo runs an alarm command (like an abrupt power-down), it should leave a message in the syslogs, just to let you know that an alarm condition got tripped. Usually you can catch this message immediately after reboot by doing "grep mondo /var/log/messages" and checking near the end of output.
To configure mondo properly (so it doesn't do this all the time), see the answer to question (8).