Now let's make all easier for this issue. Detect your USB device...
[mythcat@desk ~]$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
...
sdb 8:16 1 984M 0 disk
└─sdb1 8:17 1 983M 0 part
Be sure the USB drive has bootable flag enable:
[mythcat@desk Downloads]$ sudo fdisk /dev/sdb
Welcome to fdisk (util-linux 2.34).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): a
Selected partition 1
The bootable flag on partition 1 is disabled now.
Command (m for help): a
Selected partition 1
The bootable flag on partition 1 is enabled now.
Command (m for help): q
Umount your USB drive, do not remove it.
[mythcat@desk ~]$ sudo umount /dev/sdb
Copy the Fedora file image iso to the USB device with the dd command:
[mythcat@desk ~]$ sudo dd if=Fedora-Server-netinst-x86_64-31-1.9.iso of=/dev/sdb
1331200+0 records in
1331200+0 records out
681574400 bytes (682 MB, 650 MiB) copied, 383.766 s, 1.8 MB/s
You can test it with the qemu tool:
[mythcat@desk ~]$ sudo qemu-system-x86_64 -hda /dev/sdb