I am trying to test an unofficial LFS 7.4 live cd iso image.I downloaded it from here,https://susestudio.com/a/STQFtZ/un-o...fs-livecd-7-4#, after
cloning it and adding "logo" and "setup image of my choice".

I used "Linux live usb creator" to make the usb bootable, but when i boot from the usb i get directed to grub screen instead of setup splash screen as is appearing on "test drive" in "Suse stdio". I don't know the sequence of command or the exact command to proceed from here.Can someone give the command to install from grub screen?

I have also used "UNetBooting" to make it bootable,but after using the bootable usb made from it, it just starts looping during boot time with only "default option" to choose, which does nothing.

Also, i already have ubuntu 13.10 saucy salamnder installed as host with two more partitions not including the root partition for lfs installion purpose.

Is there other way to make bootable usb for lfs>7.0 versions or lfs7.4 in my case?Then please specify the steps?

I don't know anything about that live CD you mentioned. Sorry. But did you mean the commands to boot the system on the USB from a grub menu? If so, and if you think the system is capable of booting now, then try this...

1. At the GRUB menu, press the 'c' key to get a grub> prompt.

2. For GRUB 2, enter something in this format (you substitute the proper information, the Tab key is very handy for that)...3. If there is an initrd or initramfs file in /boot, enter at the next grub> prompt something in this format...4. Finally, enter...If it fails to boot, consider reviewing its /etc/fstab file for wrong device names or UUIDs or LABELs.

Anyway, if it does boot, then install its bootloader in the MBR of the USB drive in the usual way with grub-install. But be careful to understand what you are targeting when you do that to avoid busting the host computer's boot loader.

Lastly, you should edit grub.cfg and /etc/fstab to use UUIDs or LABELs instead of device names for a system on a USB drive since device names for those can be unpredictable. In grub.cfg, change the linux command line to use UUID or LABEL in the root= kernel parameter. To get rid of the device name in grub.cfg's set root= command, replace that command with a search command that uses --label or --fs-uuid and --set-root=<UUID or LABEL>. To use UUIDs or LABELs in grub.cfg, you have to use an initial ram filesystem. If the USB system does not already have one, then see the BLFS book for the easy steps to create one.

Anyway, these are the things I do to boot a system on a USB drive. If I misunderstood the question, then no harm was done just making you read some unhelpful stuff.