GRUB application

GRUB application

• CentOS 6 boot process:
  POST –> Boot Sequence(BIOS) –> Boot Loader (MBR) –> Kernel(ramdisk) –> rootfs –> switchroot –> /sbin/init –>(/etc/inittab, /etc/init/*.conf) –> set the default run level –> system initialization script –> close or start the corresponding level Service–>Start the terminal
• GRUB (Boot Loader): boot loader, program
  1grub: GRand Unified Bootloader
  grub 0.x: grub legacy
  grub 1.x: grub2
  2.grub legacy:
  stage1: mbr
  stage1_5: the sector after mbr, so that the bootloader in stage1 can recognize the file system on the partition where stage2 is located;
  stage2: disk partition ( /boot/grub/)
  Configuration file: /boot/grub/grub.conf <-- /etc/grub.conf
  The stage2 and kernel are usually placed in a basic disk partition;
  Function:< br>(1) Provide menu and interactive interface
  e: edit mode, used to edit menu;
  c: command mode, interactive interface;
  (2) load the kernel or Operating system
  Allows to pass parameters to the kernel
  Can hide this menu
  (3) Provides a protection mechanism for the menu
  Authentication for editing the menu
  Authentication for enabling the kernel or operating system
  3. The command line interface of grub:

  help: Get help list
   help KEYWORD: Detailed help information
   find (hd#,#)/PATH/TO/SOMEFILE:
   root (hd#,#)
   kernel /PATH/TO/KERNEL_FILE: Set the kernel file used during this boot; you can also add many cmdline parameters that the kernel supports;
   For example: init=/path/to/init, selinux=0
   initrd /PATH/TO/INITRAMFS_FILE: set the ramdisk to provide additional files for the selected kernel;
   boot: boot the selected kernel Kernel; 
   Manually start the system on the grub command line interface: 
   grub> root (hd#,#)
   grub> kernel /vmlinuz-VERSION-RELEASE ro root=/dev/DEVICE 
   grub> initrd /initramfs-VERSION-RELEASE.img
   grub> boot
   Identify hard disk device:
   (hd#,#)
   hd#: Disk number, use numbers Representation; numbering from 0
   #: partition number, represented by numbers; numbering from 0
   (hd0,0)

  4. Install grub:
  (1) grub-install
  grub-install –root-directory=ROOT /dev/DISK
  (2) grub
  grub> root (hd#,#)
  grub> setup (hd#)< br>grub legacy configuration file
  Configuration file: /boot/grub/grub.conf

  Configuration item:
   default=#: Set the default boot menu item; place a single item (title ) Numbering starts from 0; 
   timeout=#: Specify the length of time the menu item waits for option selection; 
   splashimage=(hd#,#)/PATH/ TO/XPM_PIC_FILE: specify the path of the menu background picture file; 
   hiddenmenu: hide the menu; 
   password [--md5] STRING: menu editing certification; 
   title TITLE: define the menu item "title", It can appear multiple times; 
   root (hd#,#): grub searches for stage2 and the device partition where the kernel file is located; it is the "root" of grub; 
   kernel /PATH/TO/VMLINUZ_FILE [PARAMETERS]: start 
   initrd /PATH/TO/INITRAMFS_FILE: the ramfs file matched by the kernel; 
   password [--md5] STRING: authentication when starting the selected kernel or operating system;

• grub encryption:

  Generate grub password:
   grub-md5-crypt
   grub-crypt
   Crack root password:
   When starting the system, set it to run Level 1
  Enter single user mode:
   (1) Edit grub menu (select the title to be edited, and then use the e command); 
   (2) Add after the selected kernel 
   1, s, S or single are all possible; 
   (3) In the line where the kernel is located, type the "b" command;