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  <title id="title">OverlayFS 叠加镜像层与容器可写层</title>
  <desc id="desc">展示多个只读 lowerdir 镜像层与 upperdir 可写层合并为容器看到的 merged 文件系统。</desc>
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  <text x="480" y="58" text-anchor="middle" font-size="30" font-weight="700" fill="#0f172a" font-family="Arial,'Microsoft YaHei',sans-serif">OverlayFS：把多层目录合并成一个容器文件系统</text>
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    <text x="480" y="145" font-size="21" font-weight="700" fill="#991b1b">upperdir：容器可写层</text>
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    <text x="480" y="231" font-size="19" fill="#1d4ed8">lowerdir 3：应用代码层</text>
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    <text x="480" y="311" font-size="19" fill="#0369a1">lowerdir 2：运行时与依赖层</text>
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    <text x="480" y="391" font-size="19" fill="#166534">lowerdir 1：基础系统层</text>
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