With a UEFI motherboard I have, it defaults to "CSM Enabled". I'm dual booting with Win7, and both Slackware and Win7 were installed with "CSM Enabled".

I left CSM enabled, because supposedly Win7 can't be installed with "CSM Disabled", unless you do some hacking on it, but I figured out how to disable some of the VGA for Win7 once it was installed, to allow it to boot "CSM Disabled".

So now I have CSM disabled, is Slackware running in Full UEFI, or do I need to first install Slackware with CSM disabled if I want it running in Full UEFI?

No. Just boot the installation medium in EFI mode, and it will take it from there.

It all depends on how you originally installed Slackware. If you were prompted to set up ELILO instead of regular LILO, then it is in UEFI mode. If it never prompted you for that, then you are most likely running a LILO based install, which needs compatibility mode enabled to boot.

If you have it disabled and you are booting Slackware fine, you most likely booted using UEFI... unless your firmware is buggy.

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Windows 7 originally is not UEFI capable, so this is why I think the motherboard has to be set to CSM for Win7 to work. CSM is "Compatibility Support Module" and it is basically the Legacy mode (i.e. MBR compatible).

Slackware is UEFI capable and at installation it detects whether it should install in UEFI or legacy mode. But if you enabled CSM, meaning that you enabled Legacy Mode, Slackware will install in legacy mode and not use UEFI; even if you change the mode afterwards.

But, since your system is running Windows 7 in legacy mode, if you want to dual boot smoothly, then just put every OS in legacy mode (CSM enabled).

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In regards to both of your replies, I have CSM disabled in the BIOS and Slackware boots fine, I also figured out how to do this for Win7 which is disabling the VGA at boot time, which allows Win7 to boot with CSM disabled.

In my BIOS with CSM enabled, it boots either Legacy or UEFI mode, it doesn't mean with CSM enabled, a system then only boots legacy mode, or UEFI, it just uses whichever it can.

I don't beleive because CSM was enabled it meant Slack is installed in Legacy mode, because here's the other thing, when I booted/installed Slackware off of the USB, in the BIOS it will show the USB as 2 partitions, UEFI and Legacy to boot from, and I'm 99.9% sure I booted it from the UEFI parition, which I'm assuming is then a EFI install of Slack.

Now that I have Slackware installed, is there anyway to tell which mode it's installed/running in?

P.S. I just noticed I have; /sys/firmware/efi

cd /sys/firmware/efi
~ /sys/firmware/efi >ls
config_table efivars esrt fw_platform_size fw_vendor runtime runtime-map systab vars

I also have /boot/efi and in fstab I made it 'noauto'

~ >cat /etc/fstab
/dev/sda1 / ext4 defaults 1 1
/dev/sda2 /boot/efi vfat defaults,noauto 1 0
devpts /dev/pts devpts gid=5,mode=620 0 0
proc /proc proc defaults 0 0
tmpfs /dev/shm tmpfs defaults 0 0

~ >fdisk -l
Disk /dev/sda: 119.2 GiB, 128035676160 bytes, 250069680 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 12AA986B-ECD4-44F0-B031-9F032CD2ABE9

Device Start End Sectors Size Type
/dev/sda1 2048 100558847 100556800 48G Linux filesystem
/dev/sda2 100558848 100763647 204800 100M EFI System
/dev/sda3 100763648 101025791 262144 128M Microsoft reserved
/dev/sda4 101025792 250068991 149043200 71.1G Microsoft basic data

This looks like an EFI system to me...

Observe the output of it will tell you with a list of the available uefi boot entries or not
HTH
John

"modprobe efivars" might be needed before if module not loaded (lsmod)

and efibootmgr will advise it is needed and not give the list
J

my bad
modprobe efivars will deny you if not in UEFI mode
mea-cupa
john

~ > efibootmgr
BootCurrent: 0001
Timeout: 1 seconds
BootOrder: 0001,0000
Boot0000* Windows Boot Manager
Boot0001* slackware-14.2


lsmod shows
efivars 20480 1 efi_pstore

What's your question? Your output in post 5 clearly shows an efi partition and your output from the efibootmgr command also shows two entries for windows and Slackware as efi with Slackware set to boot first. If I read your posts correctly, they both boot, correct?

If you run the command below from an installed Linux system, it will give you human readable output telling you EFI boot on HDD OR Legacy boot on HDD. But we already know it's EFI?

The output of efibootmgr you posted indicates you are in UEFI mode.

Ahh that's interesting cmd, didn't know that;

~ >[ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"
EFI boot on HDD



That's what I figured, along with seeing the /path ~ /sys/firmware/efi

Thanks everyone...