Rootfs

What is rootfs?

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Rootfs is a special instance of ramfs (or tmpfs, if that's enabled), which is always present in 2.6 systems. You can't unmount rootfs for approximately the same reason you can't kill the init process; rather than having special code to check for and handle an empty list, it's smaller and simpler for the kernel to just make sure certain lists can't become empty.

rootfs是一个特殊的ramfs(或tmpfs)实例，在2.6的内核中必然存在。rootfs不能被卸载(与其添加特殊代码用来维护空的链表，不如把rootfs节点始终加入，因此便于kernel维护：简单、精炼。rootfs是ramfs的一个空实例，占用空间极小)。

Most systems just mount another filesystem over rootfs and ignore it. The amount of space an empty instance of ramfs takes up is tiny.

大部分其他的文件系统挂载(安装)于rootfs之上。一个空白ramfs所占用的内存空间总量是极小的。

If CONFIG_TMPFS is enabled, rootfs will use tmpfs instead of ramfs by default. To force ramfs, add "rootfstype=ramfs" to the kernel command line.

重要认识：

1. rootfs是特殊的ramfs(或tmpfs)