CentOS 7 EFI install media on FAT32 formatted thumb drive

sdb is our target in this example.

1. Create partition and set ESP flag

# parted /dev/sdb
GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) mklabel gpt                                                      
Warning: The existing disk label on /dev/sdb will be destroyed and all data on this disk will be lost. Do you want to continue?
Yes/No? yes                                                               
(parted) mkpart                                                           
Partition name?  []?                                                      
File system type?  [ext2]? fat32                                          
Start? 0%                                                                 
End? 100%   
(parted) set 1 esp on                                                     
(parted) p                                                                
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sdb: 17.2GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  17.2GB  17.2GB  fat32              boot, esp

(parted) q                                                                
Information: You may need to update /etc/fstab

2. Format partition with volume label (11 characters or less, app caps; eg: CENTOSEFI)

# mkfs.vfat -v -n CENTOSEFI /dev/sdb1
mkfs.fat 4.1 (2017-01-24)
Auto-selecting FAT32 for large filesystem
/dev/sdb1 has 64 heads and 32 sectors per track,
hidden sectors 0x0800;
logical sector size is 512,
using 0xf8 media descriptor, with 33550336 sectors;
drive number 0x80;
filesystem has 2 32-bit FATs and 16 sectors per cluster.
FAT size is 16368 sectors, and provides 2094848 clusters.
There are 32 reserved sectors.
Volume ID is 2710dd05, volume label CENTOSEFI  .

3. Copy ISO content to USB

# mount /repo/ISO/CentOS-7-x86_64-Everything-1810.iso /mnt/iso/
mount: /mnt/iso: WARNING: device write-protected, mounted read-only.
# mount /dev/sdb1 /mnt/usb/
# rsync -a /mnt/iso/ /mnt/usb/

4. Edit /mnt/usb/EFI/BOOT/grub.cfg to match volume label

[root@hk181vm BOOT]# diff grub.cfg grub.cfg-before 
24c24
< 	linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CENTOS7USB --- > 	linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CentOS\x207\x20x86_64 quiet
28c28
< 	linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CENTOS7USB rd.live.check --- > 	linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CentOS\x207\x20x86_64 rd.live.check quiet
33c33
< 		linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CENTOS7USB xdriver=vesa nomodeset --- > 		linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CentOS\x207\x20x86_64 xdriver=vesa nomodeset quiet
37c37
< 		linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CENTOS7USB rescue --- > 		linuxefi /images/pxeboot/vmlinuz inst.stage2=hd:LABEL=CentOS\x207\x20x86_64 rescue quiet

5. sync and umount