I used Yumi to setup a multiboot USB. When I go to my boot menu however, it doesn't show an entry for my USB stick. I know it's not an issue with the USB because when I had only Ubuntu Live USB, everything was fine. Also I have it setup with ESP and boot flags so it should be UEFI enabled.
Why could this be happening?
FYI my PC is an Acer Aspire E15.
By “boot menu”, I take it that you don't mean the BIOS device selection menu. Depending on the model of computer, you probably need to press a key to activate that menu.
E.g. on my HP Pavilion dv7, I must press the Esc key to select a boot device, else it proceeds to boot with the first available device as per my precedential list.
On some older computers, e.g. my Dell Inspiron 5100, there was no such menu. One needed to configure the precedences of boot devices from the BIOS setup interface if one wanted to boot from a different device.
In short, you probably aren't seeing the boot menu on your YUMI stick because you are continuing to boot from the first available device as per your BIOS device list.
Did you use the regular YUMI, or the UEFI YUMI BETA version? It definitely sounds like the computer's UEFI isn't letting the USB boot, maybe it's not a UEFI YUMI drive.
According to YUMI's webpage under UEFI YUMI BETA (and being beta it's probably not 100% bug-free):
Important UEFI YUMI info: You'll need to disable secure boot (if it's enabled). Also note that 32bit UEFI firmware does not work yet.
