What is system/bin and system/xbin in android M? I have few noob questions about the system/bin and system/xbin directory in Android M.

First, what is the file inside this two directories?

Next, in system/bin, the is some file looks like

-rwxr-xr-x root     shell      117136 2008-12-31 11:30 test-platform
lrwxr-xr-x root     shell             2008-12-31 11:30 time -&gt; toybox
lrwxr-xr-x root     shell             2008-12-31 11:30 timeout -&gt; toybox
lrwxr-xr-x root     shell             2008-12-31 11:30 umount -&gt; toybox


I know toybox is the app like busybox, a collection of unix command, but what does the -&gt; means here?

Third, I am getting the error /system/bin/sh: busybox: not found, is this shows that busybox is not installed? I thought toybox already serving the same function as busybox?

Appreciate if anyone could clarify my questions, thanks!
the -&gt; indicates this is a symbolic link. That's how Busybox (and similar apps) work, so other processes can refer to them by the "full fledged name" of the component they need to call.
There are different "busyboxes". The original Busybox has a binary called busybox – yours has a binary called toybox. That won't matter if one of those symlinks is addressed – but if some process tries to call busybox directly, it of course cannot find it if it's not there. To work around that, you could create another symlink to toybox: ln -s /system/bin/toybox /system/bin/busybox (in order to do that you need root and mount the /system partition read/write).