We Have A Fail!
If you see this when running ipmitool
Could not open device at /dev/ipmi0 or /dev/ipmi/0 or /dev/ipmidev/0: No such file or directory
Yet you ran it as root, /dev/ipmi0 exists, and lsmod shows all the relevant kernel modules are loaded. Does dmesg | grep 'ipmi_si' return something like this?
[ 11.357376] ipmi_si IPI0001:00: ipmi_si: probing via ACPI
[ 11.357400] ipmi_si IPI0001:00: [io 0x0ca2] regsize 1 spacing 1 irq 0
[ 11.357402] ipmi_si: Adding ACPI-specified kcs state machine
[ 11.357450] ipmi_si: Trying ACPI-specified kcs state machine at i/o address 0xca2, slave address 0x0, irq 0
[ 67.052748] ipmi_si: There appears to be no BMC at this location
If so, shut down the server. Unplug the server. Wait 30 seconds. Plug it back in. Boot the server.
It will work. This took far too long to figure out.