What is /var/empty and why is this directory used by sshd?

Question

What is /var/empty and why is this directory used by sshd?

Answer 1

It is just an empty directory, where some processes (e.g. one of sshd processes, but it could be anything else) may chroot() to ("chroot jail"). This way processes that do not need file access do not have any files to access, so their privileges cannot be abused.