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rootfs

rootfs / rootfs rw 0 0

switch_root​

  • 切换到 newroot 并调用 init 程序
    • 用在 initramfs 中，切换到真正的 rootfs
  • 必须由 PID=1 调用
  • 会移动已经挂载的 /proc, /dev, /sys, /run 到新 root
# -c /dev/console
switch_root newroot init # init args...

pivot_root​

  • 修改当前进程的 root
  • 要注意提前准备好环境
pivot_root new_root put_old

# 切换 root
mount /dev/hda1 /new-root
cd /new-root
pivot_root . old-root
exec chroot . sh < dev/console > dev/console 2>&1
umount /old-root

umount rootfs

fuser -vm /
# killall
umount -a

mkdir /tmp/tmproot
mount -t tmpfs none /tmp/tmproot
mkdir /tmp/tmproot/{proc,sys,dev,run,usr,var,tmp,oldroot}

cp -ax /{bin,etc,mnt,sbin,lib,lib64} /tmp/tmproot/
cp -ax /usr/{bin,sbin,lib,lib64} /tmp/tmproot/usr/
cp -ax /var/{account,empty,lib,local,lock,nis,opt,preserve,run,spool,tmp,yp} /tmp/tmproot/var/

mount --make-rprivate / # necessary for pivot_root to work
pivot_root /tmp/tmproot /tmp/tmproot/oldroot
for i in dev proc sys run; do mount --move /oldroot/$i /$i; done

fuser -vm /oldroot

umount /oldroot
# 操作原来 rootfs block device

# 操作完成后重新 mount
mount /dev/vda2 /oldroot
mount --make-rprivate /
pivot_root /oldroot /oldroot/tmp/tmproot
for i in dev proc sys run; do mount --move /tmp/tmproot/$i /$i; done

# 移除临时 rootfs
umount /tmp/tmproot
rmdir /tmp/tmproot

mount -a

# 启动服务

mount --make-rshared /