Accesstime

Accesstime, commonly referred to as the access time, is a timestamp stored in a filesystem’s metadata that records the last moment a resource such as a file or directory was read or accessed. It is part of the trio of timestamps often tracked for a file: access time, modification time (mtime), and change time (ctime). Access time is updated when the contents of a file are read or when metadata associated with the file is queried, depending on the filesystem and its configuration.

Accesstime is used for auditing, indexing, and data-management decisions. It can help determine which files are frequently read, guide backup strategies, or inform archival processes. Historically, some applications and backup tools relied on atime to decide what to back up or to estimate file popularity. In modern systems, however, the usefulness of accurate accesstime has diminished due to performance overhead and the availability of alternative metrics, such as file access patterns gathered by monitoring tools.

There is a close relationship between accesstime, mtime, and ctime. Access time changes on reads, while modification time updates when the file’s content changes, and change time updates when metadata changes. Because updating atime on every read can incur performance costs, many systems implement optimizations such as noatime, relatime, or lazy updates, which alter or delay atime updates to improve speed while preserving general usage semantics.

Across platforms, the concept exists under different names and mechanisms. Unix-like systems typically expose atime via APIs such as stat, while Windows provides a Last Access Time attribute. Accuracy can be affected by filesystem caching and administrator-enforced policies. Overall, accesstime remains a useful but sometimes contentious indicator of how a resource is used.