首先贴出Fedora25下/boot/grub2/grub.cfg的内容：
1 # 2 # DO NOT EDIT THIS FILE 3 # 4 # It is automatically generated by grub2-mkconfig using templates 5 # from /etc/grub.d and settings from /etc/default/grub 6 # 7 8 ### BEGIN /etc/grub.d/00_header ### 9 set pager=1 10 11 if [ -s $prefix/grubenv ]; then 12 load_env 13 fi 14 if [ "${next_entry}" ] ; then 15 set default="${next_entry}" 16 set next_entry= 17 save_env next_entry 18 set boot_once=true 19 else 20 set default="${saved_entry}" 21 fi 22 23 if [ x"${feature_menuentry_id}" = xy ]; then 24 menuentry_id_option="--id" 25 else 26 menuentry_id_option="" 27 fi 28 29 export menuentry_id_option 30 31 if [ "${prev_saved_entry}" ]; then 32 set saved_entry="${prev_saved_entry}" 33 save_env saved_entry 34 set prev_saved_entry= 35 save_env prev_saved_entry 36 set boot_once=true 37 fi 38 39 function savedefault { 40 if [ -z "${boot_once}" ]; then 41 saved_entry="${chosen}" 42 save_env saved_entry 43 fi 44 } 45 46 function load_video { 47 if [ x$feature_all_video_module = xy ]; then 48 insmod all_video 49 else 50 insmod efi_gop 51 insmod efi_uga 52 insmod ieee1275_fb 53 insmod vbe 54 insmod vga 55 insmod video_bochs 56 insmod video_cirrus 57 fi 58 } 59 60 terminal_output console 61 if [ x$feature_timeout_style = xy ] ; then 62 set timeout_style=menu 63 set timeout=5 64 # Fallback normal timeout code in case the timeout_style feature is 65 # unavailable. 66 else 67 set timeout=5 68 fi 69 ### END /etc/grub.d/00_header ### 70 71 ### BEGIN /etc/grub.d/01_users ### 72 if [ -f ${prefix}/user.cfg ]; then 73 source ${prefix}/user.cfg 74 if [ -n "${GRUB2_PASSWORD}" ]; then 75 set superusers="root" 76 export superusers 77 password_pbkdf2 root ${GRUB2_PASSWORD} 78 fi 79 fi 80 ### END /etc/grub.d/01_users ### 81 82 ### BEGIN /etc/grub.d/10_linux ### 83 menuentry 'Fedora (4.8.8-300.fc25.x86_64) 25 (Twenty Five)' --class fedora --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-4.8.6-300.fc25.x86_64-advanced-3732e5b3-67be-4efa-a64e-08e51d341084' { 84 load_video 85 set gfxpayload=keep 86 insmod gzio 87 insmod part_msdos 88 insmod ext2 89 set root='hd0,msdos6' 90 if [ x$feature_platform_search_hint = xy ]; then 91 search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos6 --hint-efi=hd0,msdos6 --hint-baremetal=ahci0,msdos6 --hint='hd0,msdos6' 3732e5b3-67be-4efa-a64e-08e51d341084 92 else 93 search --no-floppy --fs-uuid --set=root 3732e5b3-67be-4efa-a64e-08e51d341084 94 fi 95 linux16 /boot/vmlinuz-4.8.8-300.fc25.x86_64 root=UUID=3732e5b3-67be-4efa-a64e-08e51d341084 ro rhgb quiet LANG=zh_CN.UTF-8 96 initrd16 /boot/initramfs-4.8.8-300.fc25.x86_64.img 97 } 98 menuentry 'Fedora (4.8.6-300.fc25.x86_64) 25 (Twenty Five)' --class fedora --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-4.8.6-300.fc25.x86_64-advanced-3732e5b3-67be-4efa-a64e-08e51d341084' { 99 load_video 100 set gfxpayload=keep 101 insmod gzio 102 insmod part_msdos 103 insmod ext2 104 set root='hd0,msdos6' 105 if [ x$feature_platform_search_hint = xy ]; then 106 search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos6 --hint-efi=hd0,msdos6 --hint-baremetal=ahci0,msdos6 --hint='hd0,msdos6' 3732e5b3-67be-4efa-a64e-08e51d341084 107 else 108 search --no-floppy --fs-uuid --set=root 3732e5b3-67be-4efa-a64e-08e51d341084 109 fi 110 linux16 /boot/vmlinuz-4.8.6-300.fc25.x86_64 root=UUID=3732e5b3-67be-4efa-a64e-08e51d341084 ro rhgb quiet LANG=zh_CN.UTF-8 111 initrd16 /boot/initramfs-4.8.6-300.fc25.x86_64.img 112 } 113 menuentry 'Fedora (0-rescue-0c394733687b44ac9de7038631d76a55) 25 (Twenty Five)' --class fedora --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-0c394733687b44ac9de7038631d76a55-advanced-3732e5b3-67be-4efa-a64e-08e51d341084' { 114 load_video 115 insmod gzio 116 insmod part_msdos 117 insmod ext2 118 set root='hd0,msdos6' 119 if [ x$feature_platform_search_hint = xy ]; then 120 search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos6 --hint-efi=hd0,msdos6 --hint-baremetal=ahci0,msdos6 --hint='hd0,msdos6' 3732e5b3-67be-4efa-a64e-08e51d341084 121 else 122 search --no-floppy --fs-uuid --set=root 3732e5b3-67be-4efa-a64e-08e51d341084 123 fi 124 linux16 /boot/vmlinuz-0-rescue-0c394733687b44ac9de7038631d76a55 root=UUID=3732e5b3-67be-4efa-a64e-08e51d341084 ro rhgb quiet 125 initrd16 /boot/initramfs-0-rescue-0c394733687b44ac9de7038631d76a55.img 126 } 127 128 ### END /etc/grub.d/10_linux ### 129 130 ### BEGIN /etc/grub.d/20_linux_xen ### 131 132 ### END /etc/grub.d/20_linux_xen ### 133 134 ### BEGIN /etc/grub.d/20_ppc_terminfo ### 135 ### END /etc/grub.d/20_ppc_terminfo ### 136 137 ### BEGIN /etc/grub.d/30_os-prober ### 138 menuentry 'Windows 10 Enterprise (loader) (on /dev/sdb1)' --class windows --class os $menuentry_id_option 'osprober-chain-10FF15F410FF15F4' { 139 insmod part_msdos 140 insmod ntfs 141 set root='hd1,msdos1' 142 if [ x$feature_platform_search_hint = xy ]; then 143 search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1 10FF15F410FF15F4 144 else 145 search --no-floppy --fs-uuid --set=root 10FF15F410FF15F4 146 fi 147 parttool ${root} hidden- 148 drivemap -s (hd0) ${root} 149 chainloader +1 150 } 151 152 ### BEGIN /etc/grub.d/40_custom ### 153 # This file provides an easy way to add custom menu entries. Simply type the 154 # menu entries you want to add after this comment. Be careful not to change 155 # the 'exec tail' line above. 156 ### END /etc/grub.d/40_custom ### 157 158 ### BEGIN /etc/grub.d/41_custom ### 159 if [ -f ${config_directory}/custom.cfg ]; then 160 source ${config_directory}/custom.cfg 161 elif [ -z "${config_directory}" -a -f $prefix/custom.cfg ]; then 162 source $prefix/custom.cfg; 163 fi 164 ### END /etc/grub.d/41_custom ###
显然，其中没有找到传说中的
1 # boot=/dev/sda 2 default=0 3 timeout=5
所以无法通过修改grub.cfg来调整系统的默认启动顺序。不过无意中，发现可以用三条命令解决这个问题，具体代码如下：
1 # 首先找到windows的menuentry 2 cat /boot/grub2/grub.cfg | grep windows 3 # 然后设置windows作为默认的启动项 4 grub2-set-default "Windows *** " 5 # 用第一步得到的结果执行第2步 6 # 验证默认的启动项 7 grub2-editenv list
修改前后使用第三条命令的结果也同样贴出：
1 saved_entry=Fedora (4.8.8-300.fc25.x86_64) 25 (Twenty Five) 2 saved_entry=Windows 10 Enterprise (loader) (on /dev/sdb1)
这样就可以在Fedora25中修改了grub启动配置文件，下一次电脑启动时Win10将会出现在第一条，即默认启动系统。