linux下，文件有写权限却不能删除，可能是因为对文件的父目录没有写权限，因为目录是一种特殊的文件，它里面保存着目录下的文件列表，删除其下的文件，需要修改目录里面保存的信息。“一切皆文件”的思想又一次得到体现。
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