Help with creating bootable usb from iso

If the .iso is a "hybrid mode" image (like most Ubuntu and Debian images these days, have no idea about Arch), then you can just write it directly to the USB just as if it was a CD-ROM drive. For instance, using dd.

dd if=imagefile.iso of=/dev/sdc oflag=direct bs=1048576

If the .iso is not a hybrid mode image, then you can use UNetBootin, available from Ubuntu's repositories, which is an easy way to burn an ISO (for a Linux distro) to a USB key, converting its filesystem to be compatible. Note: UNetBootin is a GUI app.

First let's find out where your USB is in using the fdisk command:

sudo fdisk -l 

and you'll see a list of partitions in your computer.

sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
/dev/sda1            2048    15624191     7811072   82  Linux swap / Solaris
/dev/sda2   *    15624192    64452607    24414208   83  Linux
/dev/sdb1         1214121     3244232    42323242   84  vfat   

now you'll know that your usb is at /dev/sdb and /dev/sdb1 is the only 'partition' on it, if not per se a partition.

Now you have to do a block-by-block copy of the .iso file that you have to boot from to the disk. dd command is the one to use.

dd if=/path/to/iso.iso of=/dev/sdb

Notice that I'm using sdb here, not sdb1 or any other partition.

Now you'll be able to boot from the usb when you restart your computer. Just select to boot from the USB disk.