假設你原本的 /usr 跟 /backup 已經 mount 起來了，也都寫在 /etc/fstab 裡。
1. 進 single user mode
2. /sbin/mount -a
3. cd /usr
4. /usr/bin/tar clf - . | /usr/bin/tar xvpf - -C /backup
5. 修改 /etc/fstab，把 /backup 的 slice 掛為 /usr
（建議把原本的 /usr 改掛為 /backup，或是註解掉）
6. 重開
這是我在很早以前的作法，我沒重新確認指令的參數是否仍可用。
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