배경화면
  gnome-look.org

테마 설정
[centos@localhost ~]$ rpm -qa gnome-tweak-tool
gnome-tweak-tool-3.14.3-2.el7.noarch
[centos@localhost ~]$ gnome-t
gnome-terminal        gnome-text-editor     gnome-thumbnail-font  gnome-tweak-tool
[centos@localhost ~]$ gnome-tweak-tool 

[centos@localhost ~]$ su -c 'yum -y install grub2-starfield-theme'
암호:
Loaded plugins: fastestmirror, langpacks
Repodata is over 2 weeks old. Install yum-cron? Or run: yum makecache fast
base                                                                                  | 3.6 kB  00:00:00     
extras                                                                                | 3.4 kB  00:00:00     
extras/7/x86_64/primary_db                                                            | 139 kB  00:00:00     
Loading mirror speeds from cached hostfile
 * base: centos.mirror.cdnetworks.com
 * extras: centos.mirror.cdnetworks.com
No package grub2-starfield-theme available.
Error: Nothing to do

=>직접 다운로드
[root@localhost ~]# wget "http://download.hanbit.co.kr/centos/7/grub2-starfield-theme.rpm"

[root@localhost ~]# ls -l
합계 2208
-rw-------. 1 root root    1756  2월 27 23:57 anaconda-ks.cfg
-rw-r--r--. 1 root root 2252232  1월 12  2016 grub2-starfield-theme.rpm
-rw-r--r--. 1 root root    1787  2월 28 01:50 initial-setup-ks.cfg

[root@localhost ~]# yum -y localinstall grub2-starfield-theme.rpm 

[root@localhost ~]# gedit /etc/default/grub 

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
GRUB_THEME="/boot/grub2/themes/system/theme.txt"

[root@localhost ~]# ls /boot/grub2/themes/system/
COPYING.CC-BY-SA-3.0    boot_menu_c.png   boot_menu_se.png  terminal_box_c.png   terminal_box_se.png
DejaVuSans-10.pf2       boot_menu_e.png   boot_menu_sw.png  terminal_box_e.png   terminal_box_sw.png
DejaVuSans-12.pf2       boot_menu_n.png   boot_menu_w.png   terminal_box_n.png   terminal_box_w.png
DejaVuSans-Bold-14.pf2  boot_menu_ne.png  slider_c.png      terminal_box_ne.png  theme.txt
README                  boot_menu_nw.png  slider_n.png      terminal_box_nw.png  unicode.pf2
blob_w.png              boot_menu_s.png   slider_s.png      terminal_box_s.png

//웹 브라우저로 임의 배경이미지 다운로드 후 ball.jpg 저장
[root@localhost ~]# ls ~centos/
Firefox_wallpaper.png  ball.jpg  공개  다운로드  문서  바탕화면  비디오  사진  서식  음악
[root@localhost ~]# mv /home/centos/ball.jpg  /boot/grub2/themes/system/

[root@localhost ~]# vi /boot/grub2/themes/system/theme.txt

#general settings
message-font: "DejaVu Sans Regular 12"
message-color: "#fff"
message-bg-color: "#000"
terminal-box: "terminal_box_*.png"
desktop-image: "ball.jpg"

배경 이미지 이름 변경 적용
[root@localhost ~]# grub2-mkconfig -o /boot/grub2/grub.cfg