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耍耍OverlayFS
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自Linux3.4之后，就可以使用overlay了。来，耍耍。
[email protected]:~/playoverlay$ mkdir lower{1,2,3} upper work merged # 创建文件夹 [email protected]:~/playoverlay$ touch lower1/l1.txt lower2/l2.txt lower3/l3.txt # 创建文件 [email protected]:~/playoverlay$ tree # 这是目前的结构 . ├── lower1 │ └── l1.txt ├── lower2 │ └── l2.txt ├── lower3 │ └── l3.txt ├── merged ├── upper └── work 6 directories, 3 files [email protected]:~/playoverlay$ sudo mount -t overlay overlay -o lowerdir=./lower1:./lower2:./lower3,upperdir=./upper,workdir=./work ./merged/ # 挂载 [email protected]:~/playoverlay$ tree # 这是目前的结构 . ├── lower1 │ └── l1.txt ├── lower2 │ └── l2.txt ├── lower3 │ └── l3.txt ├── merged │ ├── l1.txt │ ├── l2.txt │ └── l3.txt ├── upper └── work └── work [error opening dir] 7 directories, 6 files [email protected]:~/playoverlay$ touch merged/hahahahhha # 创建一个文件 [email protected]:~/playoverlay$ rm merged/l1.txt # 删除一个文件 [email protected]:~/playoverlay$ tree . ├── lower1 │ └── l1.txt ├── lower2 │ └── l2.txt ├── lower3 │ └── l3.txt ├── merged │ ├── hahahahhha │ ├── l2.txt │ └── l3.txt ├── upper │ ├── hahahahhha │ └── l1.txt └── work └── work [error opening dir] 7 directories, 8 files [email protected]:~/playoverlay$
解释两点：
-
sudo mount -t overlay overlay -o lowerdir=./lower1:./lower2:./lower3,upperdir=./upper,workdir=./work ./merged/:./merged/
- 如果我们直接删除lower2里的文件会怎样呢？
[email protected]:~/playoverlay$ tree . ├── lower1 │ └── l1.txt ├── lower2 │ └── l2.txt ├── lower3 │ └── l3.txt ├── merged │ ├── hahahahhha │ ├── l2.txt │ └── l3.txt ├── upper │ ├── hahahahhha │ └── l1.txt └── work └── work [error opening dir] 7 directories, 8 files [email protected]:~/playoverlay$ rm lower2/l2.txt [email protected]:~/playoverlay$ tree . ├── lower1 │ └── l1.txt ├── lower2 ├── lower3 │ └── l3.txt ├── merged │ ├── hahahahhha │ └── l3.txt ├── upper │ ├── hahahahhha │ └── l1.txt └── work └── work [error opening dir] 7 directories, 6 files [email protected]:~/playoverlay$
当然是上边就看不到了。
实现，就去看下边的 overlay.txt，用法，就看ArchWiki和Docker那个文档，就不赘述了。另外：
- 可以使用mount打印出当前挂载的overlayfs
- 用Docker起容器之后，可以用mount打印出挂载的overlayfs，然后探索探索Docker是怎么使用overlayfs的
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