SD卡自动扩容

理解SD卡自动扩容工作原理

补充内容

• 刚烧录完系统时候，第一次启动时候，init进程执行的是resize的脚本
• /boot/cmdline.txt
  • console=serial1,115200 console=tty1 root=PARTUUID=1d1c0dec-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet init=/usr/lib/raspi-config/init_resize.sh splash plymouth.ignore-serial-consoles
    • init=/usr/lib/raspi-config/init_resize.sh

steps

• sudo raspi-config
  • Advanced Options
    • Expand Filesystem
• /usr/bin/raspi-config

  do_expand_rootfs() {
    # -h : FILE exists and is a symbolic link (same as -L)
    if ! [ -h /dev/root ]; then
      whiptail --msgbox "/dev/root does not exist or is not a symlink. Don't know how to expand" 20 60 2
      return 0
    fi
  
    # readlink用来找出符号链接所指向的位置。 
    ROOT_PART=$(readlink /dev/root)
    # 从变量$string的开头, 删除最短匹配$substring的子串
    PART_NUM=${ROOT_PART#mmcblk0p}
    if [ "$PART_NUM" = "$ROOT_PART" ]; then
      whiptail --msgbox "/dev/root is not an SD card. Don't know how to expand" 20 60 2
      return 0
    fi
  
    # NOTE: the NOOBS partition layout confuses parted. For now, let's only 
    # agree to work with a sufficiently simple partition layout
    if [ "$PART_NUM" -ne 2 ]; then
      whiptail --msgbox "Your partition layout is not currently supported by this tool. You are probably using NOOBS, in which case your root filesystem is already expanded anyway." 20 60 2
      return 0
    fi
  
    # 再次确认分区表和设备节点提取的数值是否一致
    # 
    # shell script:
    #   root@zengjf:/home/zengjf/hacking# parted /dev/sdb -ms unit s p 
    #   BYT;
    #   /dev/sdb:1953525168s:scsi:512:4096:gpt:ATA ST1000LM035-1RK1:;
    #   1:2048s:943720448s:943718401s:ntfs:Basic data partition:msftdata;
    #   2:943722496s:1953523711s:1009801216s:ntfs:Basic data partition:msftdata;
    LAST_PART_NUM=$(parted /dev/mmcblk0 -ms unit s p | tail -n 1 | cut -f 1 -d:)
    if [ "$LAST_PART_NUM" != "$PART_NUM" ]; then
      whiptail --msgbox "/dev/root is not the last partition. Don't know how to expand" 20 60 2
      return 0
    fi
  
    # Get the starting offset of the root partition
    # 获取文件系统分区起始位置
    PART_START=$(parted /dev/mmcblk0 -ms unit s p | grep "^${PART_NUM}" | cut -f 2 -d:)
    [ "$PART_START" ] || return 1
    # Return value will likely be error for fdisk as it fails to reload the
    # partition table because the root fs is mounted
    fdisk /dev/mmcblk0 <<EOF
  p
  d
  $PART_NUM
  n
  p
  $PART_NUM
  $PART_START
  
  p
  w
  EOF
    ASK_TO_REBOOT=1
  
    # now set up an init.d script
  cat <<\EOF > /etc/init.d/resize2fs_once &&
  #!/bin/sh
  ### BEGIN INIT INFO
  # Provides:          resize2fs_once
  # Required-Start:
  # Required-Stop:
  # Default-Start: 2 3 4 5 S
  # Default-Stop:
  # Short-Description: Resize the root filesystem to fill partition
  # Description:
  ### END INIT INFO
  . /lib/lsb/init-functions
  case "$1" in
    start)
      log_daemon_msg "Starting resize2fs_once" &&
      resize2fs /dev/root &&                       # 真正调整大小的地方
      rm /etc/init.d/resize2fs_once &&             # 删除文件，表明该文件只能被运行一次
      update-rc.d resize2fs_once remove &&
      log_end_msg $?
      ;;
    *)
      echo "Usage: $0 start" >&2
      exit 3
      ;;
  esac
  EOF
    chmod +x /etc/init.d/resize2fs_once &&         # 给出下次运行的权限
    update-rc.d resize2fs_once defaults &&         # 默认运行
    if [ "$INTERACTIVE" = True ]; then
      whiptail --msgbox "Root partition has been resized.\nThe filesystem will be enlarged upon the next reboot" 20 60 2
    fi
  }