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How do I determine whether a particular running Ubuntu system was booted using EFI/UEFI, or BIOS?

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Interesting question. Not an exact dupe but try the answer here, to a similar question. –  Tom Brossman Jul 11 '12 at 21:10
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2 Answers 2

up vote 16 down vote accepted

The easiest way is to check to see if /sys/firmware/efi exists. It does not appear if you booted using traditional BIOS.

#!/bin/bash
[ -d /sys/firmware/efi ] && echo UEFI || echo BIOS
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Note: The below is a deprecated method that may not always work. Instead, please see Colin's answer using /sys/firmware/efi just above or below this one.


It's very easy to tell if a system was booted in EFI (or not, in which case it must be BIOS):

Just use 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.

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I'd simplify that to if dmesg | grep -Fq "EFI v"; then .... No point in running the [ command in addition, just to test for success/failure. $? is mainly useful for checking for specific errors. –  geirha Jul 12 '12 at 10:50
2  
This is brittle, as there is no guarantee that the string searched for is generated by the desired feature. –  Thorbjørn Ravn Andersen Jul 13 '12 at 1:28
    
@ThorbjørnRavnAndersen: The Ubuntu Developer Summit folks seem to think it's part of the specification...can you provide a source or reference for your contention? –  izx Jul 13 '12 at 1:30
1  
@izx, any script can happen to write "EFI v" as part of something else. If that happens on a BIOS machine, this would be a false positive. –  Thorbjørn Ravn Andersen Jul 13 '12 at 1:37
2  
Best not to grep for text in the kernel log, it is subject to change. Best to look at /sys/firmware/efi –  Colin Ian King Jul 27 '12 at 18:24
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