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NuttX does, however, support Linux-like special device node, character driver, and block driver files (as well as NuttX-specific mountpoint, named semaphore, message queue, and shared memory special files). However, these are not special files in sense that the term special files is used in a POSIX environment: In NuttX these special files may only be created in the root pseudo-file system. For the case of device nodes, see Device Nodes for further information.

In NuttX, the underlying principle is that all named resources appear as special files in the root pseudo-file system and are managed by the VFS.

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mkdir can only work if there is a real filesystem at the location.
There are no real directories in the psuedo-filesystem.
The pseudo-filesystem does support nodes that look like directories and have some of the properties of directories (like the node /mnt mentioned above).
But this is really an illusion.
I suppose that one could add the capability to create new, empty nodes in the pseudo-filesystem using 'mkdir' –
but I am not sure that this would really serve any purpose other than completing the illusion.

\[On the other hand, all directories are really an _illusion_ in a way and I suppose that in that sense these nodes the pseudo-filesystem are just as _real_ as any other directory.]

After you mount the SD card at /mnt/sda, then you can do:

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