Hiya trying to boot my 27inch 2010 iMac from a bootable usb drive but it get stuck on this can anyone help? Is it normal, how long does it take. Thanks in advance.
looks like you booted in single-user mode (by pressing cmd-s at startup).
If so, type :
exit
Press enter and the Mac should boot (but in single user mode).
For booting from an external drive , keeping pressed option at startup is all you need to get to the bootable drives.
Select a drive and press enter.