rhel7.2采用的grub作为引导程序，所以和以前版本不同，并不是修改/etc/grub.conf来修改启动项，需要如下操作：
1、查看可以修改的内核选项

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[root@localhost ~]# cat /boot/grub2/grub.cfg |grep menuentry
if [ x"${feature_menuentry_id}" = xy ]; then
menuentry_id_option="--id"
menuentry_id_option=""
export menuentry_id_option
menuentry 'Red Hat Enterprise Linux Server (4.4.0) 7.2 (Maipo)' --class red --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-327.el7.x86_64-advanced-4becb360-5f46-4607-9408-285eec7c39cc' {
menuentry 'Red Hat Enterprise Linux Server (3.10.0-327.el7.x86_64) 7.2 (Maipo)' --class red --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-327.el7.x86_64-advanced-4becb360-5f46-4607-9408-285eec7c39cc' {
menuentry 'Red Hat Enterprise Linux Server (0-rescue-5bb9b453915c4d5cbabb3f776aaadec4) 7.2 (Maipo)' --class red --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-5bb9b453915c4d5cbabb3f776aaadec4-advanced-4becb360-5f46-4607-9408-285eec7c39cc' {
[root@localhost ~]#

2、修改默认内核

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[root@localhost ~]# grub2-set-default "Red Hat Enterprise Linux Server (4.4.0) 7.2 (Maipo)"

3、验证是否成功，并重启服务器

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rhel7.2 修改内核启动顺序