GRUB2

GRUB2 uses a more programmatic approach in the way the menu is presented. At first glance, GRUB2 may look intimidating, but rest assured that it's not as complicated as it appears to be. The syntax is similar to a programming language, with lots of if...then statements. Here is what /boot/grub/grub.cfg looks like on a CentOS 7 system:

[root@localhost ~]# cat /boot/grub2/grub.cfg
 #
 # DO NOT EDIT THIS FILE
 #
 # It is automatically generated by grub2-mkconfig using templates
 # from /etc/grub.d and settings from /etc/default/grub
 #
### BEGIN /etc/grub.d/00_header ###
 set pager=1
if [ -s $prefix/grubenv ]; then
 load_env
 fi
 if [ "${next_entry}" ] ; then
 set default="${next_entry}"
 set next_entry=
 save_env next_entry
 set boot_once=true
 else
 set default="${saved_entry}"
 fi

Some of the following output is omitted for the sake of brevity in /boot/grub/grub.cfg:

### BEGIN /etc/grub.d/10_linux ###
 menuentry 'CentOS Linux (3.10.0-693.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-693.el7.x86_64-advanced-16e2de7b-b679-4a12-888e-55081af4dad8' {
 load_video
 set gfxpayload=keep
 insmod gzio
 insmod part_msdos
 insmod xfs
 set root='hd0,msdos1'
 if [ x$feature_platform_search_hint = xy ]; then
 search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 --hint='hd0,msdos1' 40c7c63f-1c93-438a-971a-5331e265419b
 else
 search --no-floppy --fs-uuid --set=root 40c7c63f-1c93-438a-971a-5331e265419b
 fi
 linux16 /vmlinuz-3.10.0-693.el7.x86_64 root=UUID=16e2de7b-b679-4a12-888e-55081af4dad8 ro crashkernel=auto rhgb quiet LANG=en_US.UTF-8
 initrd16 /initramfs-3.10.0-693.el7.x86_64.img
 }
 ### END /etc/grub.d/10_linux ###

So, to interpret the /boot/grub/grub.cfg file, we look for lines that start with menuentry. These lines start the actual menu entry for an operating system, such as a Linux distribution or a Windows OS.