iused

iused is a term used in Unix-like computing to describe the number of inodes currently in use on a filesystem. An inode is a data structure that stores metadata about a file or directory, including ownership, permissions, size, and pointers to data blocks. Each distinct file or directory consumes one inode, and filesystems allocate a fixed total number of inodes. When inodes are exhausted, new files cannot be created even if there is free disk space.

In many BSD-derived environments, iused also refers to a small command-line utility that reports inode usage for mounted filesystems. The utility is designed to help administrators monitor inode pressure and capacity. Typical functionality includes reporting the number of inodes used and available per filesystem, and, on some implementations, per directory or mount point. Usage syntax and options can vary by implementation, but common forms involve invoking iused with a target filesystem or with a flag to display all mounted filesystems.

Implementation details and availability vary by operating system and version. On Linux systems, inode usage can often be examined with built-in tools such as df -i or statvfs calls rather than a dedicated iused binary. In macOS and some BSDs, a dedicated iused tool may be present in certain toolkits or developer packages, but it is not guaranteed to be installed by default on all systems. When present, it serves as a concise, purpose-built aid for capacity planning and troubleshooting inode-related issues.

See also: inode, df -i, statvfs, filesystem.