The chroot command runs a command or process with a different root directory than the system's actual root. This creates an isolated environment where the process cannot access files outside the specified directory tree. It's commonly used for system recovery, testing, and security isolation. Option B is wrong because chroot uses a DIFFERENT root, not the same. Option C is incomplete - it runs with a different root, not necessarily in the actual root directory. Option D mentions /opt which is unrelated to chroot's purpose.