Nmount

Nmount is a system call used by several BSD-derived operating systems to perform filesystem mounting via a flexible, option-based interface. It provides a more general mechanism than the traditional mount interface by accepting a list of key-value options encoded in an array of iovec structures, allowing new options to be added without changing the syscall signature.

The typical prototype is int nmount(const struct iovec iov, int iovcnt, int flags), where iov describes a sequence of name/value strings. A mount is described by a set of name/value pairs that specify the filesystem type, the target mount point, the source device or filesystem descriptor, and various mount options such as read-only, nosuid, or other filesystem-specific flags.

Implementations: Nmount is implemented in several BSD-family operating systems, including OpenBSD, NetBSD, and DragonFly BSD, where it underpins a modernized mounting interface. It is not part of the Linux kernel, where the legacy mount interface remains predominant; Linux provides different APIs for mounting and for handling mount options.

Usage: System utilities such as mount can utilize nmount to support mounting different filesystem types in a unified way. The userland wrapper translates traditional mount commands into iovec-based calls on supported platforms.

Portability and security: Because it is a kernel-level interface, nmount requires appropriate privileges (such as root) and its availability varies by OS version and flavor. Software wishing to use it should consult the target system’s manual pages for exact semantics and option names.