主机系统开机流程
boot loader 主要功能
显示核心模块加载信息
查询模块信息
核心模块的加载与移除
boot loader 的两个 stage
grup2配置文件 /boot/grub2/grub.cfg
grub2识别磁盘
grub2 配置文件 /etc/default/grub 和 /etc/grub.d
[root@localhost grub.d]# 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 if [ x"${feature_menuentry_id}" = xy ]; then menuentry_id_option="--id" else menuentry_id_option="" fi export menuentry_id_option if [ "${prev_saved_entry}" ]; then set saved_entry="${prev_saved_entry}" save_env saved_entry set prev_saved_entry= save_env prev_saved_entry set boot_once=true fi function savedefault { if [ -z "${boot_once}" ]; then saved_entry="${chosen}" save_env saved_entry fi } function load_video { if [ x$feature_all_video_module = xy ]; then insmod all_video else insmod efi_gop insmod efi_uga insmod ieee1275_fb insmod vbe insmod vga insmod video_bochs insmod video_cirrus fi } terminal_output console if [ x$feature_timeout_style = xy ] ; then set timeout_style=menu set timeout=5 # Fallback normal timeout code in case the timeout_style feature is # unavailable. else set timeout=5 fi ### END /etc/grub.d/00_header ### ### BEGIN /etc/grub.d/00_tuned ### set tuned_params="" set tuned_initrd="" ### END /etc/grub.d/00_tuned ### ### BEGIN /etc/grub.d/01_users ### if [ -f ${prefix}/user.cfg ]; then source ${prefix}/user.cfg if [ -n "${GRUB2_PASSWORD}" ]; then set superusers="root" export superusers password_pbkdf2 root ${GRUB2_PASSWORD} fi fi # END /etc/grub.d/01_users ### ▽ ### BEGIN /etc/grub.d/10_linux ### menuentry 'CentOS Linux (3.10.0-957.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-957.el7.x86_64-advanced-ccdda529-f59c-4990-9165-b6d1cd522034' { load_video set gfxpayload=keep insmod gzio insmod part_msdos insmod xfs set root='hd0,msdos1' if [ x$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' ba80a371-e434-431e-9508-df4b2827efad else search --no-floppy --fs-uuid --set=root ba80a371-e434-431e-9508-df4b2827efad fi linux16 /vmlinuz-3.10.0-957.el7.x86_64 root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet LANG=zh_CN.UTF-8 initrd16 /initramfs-3.10.0-957.el7.x86_64.img } menuentry 'CentOS Linux (0-rescue-f7819fbfbe0b4074b5dfebfab540afcb) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-f7819fbfbe0b4074b5dfebfab540afcb-advanced-ccdda529-f59c-4990-9165-b6d1cd522034' { load_video insmod gzio insmod part_msdos insmod xfs set root='hd0,msdos1' if [ x$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' ba80a371-e434-431e-9508-df4b2827efad else search --no-floppy --fs-uuid --set=root ba80a371-e434-431e-9508-df4b2827efad fi linux16 /vmlinuz-0-rescue-f7819fbfbe0b4074b5dfebfab540afcb root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet initrd16 /initramfs-0-rescue-f7819fbfbe0b4074b5dfebfab540afcb.img } ### END /etc/grub.d/10_linux ### ### BEGIN /etc/grub.d/20_linux_xen ### ### END /etc/grub.d/20_linux_xen ### ### BEGIN /etc/grub.d/20_ppc_terminfo ### ### END /etc/grub.d/20_ppc_terminfo ### ### BEGIN /etc/grub.d/30_os-prober ### ### END /etc/grub.d/30_os-prober ### ### BEGIN /etc/grub.d/40_custom ### # This file provides an easy way to add custom menu entries. Simply type the # menu entries you want to add after this comment. Be careful not to change # the 'exec tail' line above. ### END /etc/grub.d/40_custom ### ### BEGIN /etc/grub.d/41_custom ### if [ -f ${config_directory}/custom.cfg ]; then source ${config_directory}/custom.cfg elif [ -z "${config_directory}" -a -f $prefix/custom.cfg ]; then source $prefix/custom.cfg; fi ### END /etc/grub.d/41_custom ### [root@localhost grub.d]# vim /etc/grub.d/40_custom #!/bin/sh exec tail -n +3 $0 # This file provides an easy way to add custom menu entries. Simply type the # menu entries you want to add after this comment. Be careful not to change # the 'exec tail' line above. menuentry 'My graphical Centos' --class centos --class gnu-linux --class gnu --class os --unrestricted --id 'mygraphical' $menuentry_id_option 'gnulinux-3.10.0-957.el7.x86_64-advanced-ccdda529-f59c-4990-9165-b6d1cd522034' { load_video set gfxpayload=keep insmod gzio insmod part_msdos insmod xfs set root='hd0,msdos1' if [ x$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' ba80a371-e434-431e-9508-df4b2827efad else search --no-floppy --fs-uuid --set=root ba80a371-e434-431e-9508-df4b2827efad fi linux16 /vmlinuz-3.10.0-957.el7.x86_64 root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet LANG=zh_CN.UTF-8 systemd.unit=graphical.target initrd16 /initramfs-3.10.0-957.el7.x86_64.img } ~ "40_custom" 20L, 1185C 已写入 [root@localhost grub.d]# grub2-mkconfig -o /boot/grub2/grub.cfg Generating grub configuration file ... Found linux image: /boot/vmlinuz-3.10.0-957.el7.x86_64 Found initrd image: /boot/initramfs-3.10.0-957.el7.x86_64.img Found linux image: /boot/vmlinuz-0-rescue-f7819fbfbe0b4074b5dfebfab540afcb Found initrd image: /boot/initramfs-0-rescue-f7819fbfbe0b4074b5dfebfab540afcb.img done [root@localhost grub.d]# reboot
选择之后就会直接进入我们的图形界面
设置默认开机画面为字符
[root@localhost /]# sudo systemctl set-default multi-user.target Removed symlink /etc/systemd/system/default.target. Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target.
以前我们设置的默认开机方式是图形界面，经过上面设置之后，默认设置就变成了命令行模式。
但是当我们选择第三项，我们自己的设置的时候，他还是会进入图形界面。有点意思。
透过chainloader 的方式移交lader 控制权
上面主要介绍的做双系统的相关知识（我觉得），还是需要实践，看是看不会的。。。。下面有时间会找台机器做测试。来做双系统试一下