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= 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=
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
set timeout=
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--df4b2827efad
else
search --no-floppy --fs-uuid --set=root ba80a371-e434-431e--df4b2827efad
fi
linux16 /vmlinuz-3.10.-.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-
initrd16 /initramfs-3.10.-.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--df4b2827efad
else
search --no-floppy --fs-uuid --set=root ba80a371-e434-431e--df4b2827efad
fi
linux16 /vmlinuz--rescue-f7819fbfbe0b4074b5dfebfab540afcb root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet
initrd16 /initramfs--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 + $
# 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--df4b2827efad
else
search --no-floppy --fs-uuid --set=root ba80a371-e434-431e--df4b2827efad
fi
linux16 /vmlinuz-3.10.-.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- systemd.unit=graphical.target
initrd16 /initramfs-3.10.-.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.-.el7.x86_64
Found initrd image: /boot/initramfs-3.10.-.el7.x86_64.img
Found linux image: /boot/vmlinuz--rescue-f7819fbfbe0b4074b5dfebfab540afcb
Found initrd image: /boot/initramfs--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
