How do I determine whether a particular running Ubuntu system was booted using EFI/UEFI, or BIOS?
The answer below is a method that may not always work.
Instead use Colin's answer based on
It's very easy to tell if a system was booted in EFI (or not, in which case it must be BIOS):
dmesg | grep "EFI v"
This will return a line like this, if the system was booted off of EFI:
[ 0.000000] EFI v2.00 by American Megatrends
Or return nothing if it was not, in which case it was booted off of BIOS
Example of bash script usage based on grep's exit code:
... dmesg | grep -q "EFI v" # -q tell grep to output nothing if [ $? -eq 0 ] # check exit code; if 0 EFI, else BIOS then echo "You are using EFI boot." else echo "You are using BIOS boot" fi ...
Source: For how to determine if an EFI system is using legacy-BIOS emulation or not, as well as more information on testing for EFI and EFI compatibility, along with the strings for a number of EFI vendors/versions, please see this page from the Ubuntu Developer Summit for Precise.