ISO image created using UNetbootin under Ubuntu 16.04 for USB flash drive appears: Missing Operating System (mbr.bin)

Troubleshooting is done in the following ways:

1, determine whether the USB stick really has a boot system

2, whether the partition has been marked as active, especially when using Fdisk for partitioning, if the partition is >=2, the activation partition is not set by default.

For example, here is how to set the partition activation state via FDISK:

#分区操作, the hard drive specified as/dev/sda
fdisk/dev/SDA
 for Help ): a
#选择第几个分区Partition Number (11
#将操作写入磁盘  forW

Reference:

http://www.syslinux.org/wiki/index.php?title=Common_Problems#Missing_Operating_System_.28mbr.bin.29

https://ubuntuforums.org/showthread.php?t=2171393

ISO image created using UNetbootin under Ubuntu 16.04 for USB flash drive appears: Missing Operating System (mbr.bin)