Ubuntu MATE on INTEL-iMac late 2006

I tried to install Ubuntu-MATE 14.04 (ubuntu-mate-14.04.2-LTS-desktop-amd64+mac.iso) on my iMac late2006 (core2duo 2.16GHz), which had been retired recently.
Ubuntu was installed with pure EFI booting instead of Bootcamp because OSX was no longer used.  Unlike the case of PPC-Mac, the installation was easily done.

But, the long-time whiteout screen appears before booting when turn on the power.  According to here,  this boot delay occurs when installed by Mac-EFI mode.  Immediately, I tried to remove the boot delay by this instruction.

However, I couldn't run efibootmgr because "modprobe efivars" was never effected.

Next, I tried easyUEFI on bootable windowsPE, but the bootable disk created by easyUEFI didn't boot on my iMac. 

The Bootcamp mode (MBR) rather than EFI mode seems to be troubleless when using ubuntu on Intel-Mac.