Chroot

<operating system> The UNIX command to make the root directory (/) become something other than its default for the lifetime of the current process.

It can only be run by privileged users and is used to give a process (commonly a network server such as FTP or HTTP) access to a restricted portion of the file system.

The new root contains copies of all the essential files and directories, e.g. /lib, /dev/tty, /tmp.