fileatime

Fileatime, in the context of Unix-like operating systems, refers to the access time attribute of a file. It is the timestamp that records the last moment a file was read or accessed, and it is typically stored in the file’s inode as the atime field (often exposed via the stat system call as st_atime).

Conceptually, atime tracks when a file was last used, complementing other timestamps such as mtime (modification time) and ctime (status change time). Access time updates occur when the file is read or executed, though the exact behavior can depend on the filesystem and mounting options. Some workflows rely on atime for auditing or backup purposes, while others disable it to avoid extra disk I/O.

Performance considerations have led to the adoption of mount options that influence atime updates. The noatime option disables atime updates entirely, improving performance on read-heavy workloads. How atime is updated defensively is addressed by options such as relatime, strictatime, and lazytime. Relatime reduces the frequency of atime writes by updating atime only under certain conditions, typically when the file has been modified since the last atime or after a time interval has elapsed. Strictatime enforces atime updates with each access, preserving historical semantics. Lazytime and related approaches provide further optimizations on when atime is written.

Filesystem support varies, but most modern Linux filesystems (such as ext4, XFS, btrfs) support atime and these mount options. Network filesystems and some older or alternative systems may implement different semantics for atime updates, which can affect consistency guarantees and performance.

See also: atime, mtime, ctime, relatime, noatime, strictatime, lazytime.