Why does FHS have a usr directory

It appears you can 开发者_如何学编程put all you need in /bin so why do we bother with the /usr/bin directory?

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/bin is supposed to reside on the root filesystem, whereas /usr may be an alternate filesystem - even network mounted (multiple boxes sharing the same /usr).

This means that any essential basic utilities you need to bring up the system and mount filesystems, including troubleshooting, should live in /bin. Everything non-essential can go in /usr.