strictatime

Strictatime is a mount option used in Linux filesystems to ensure that the access time (atime) of a file is updated on every read operation. By default, many modern filesystems apply atime optimizations (such as relatime) to reduce disk writes, which means atime may not be updated on every access. Enabling strictatime disables these optimizations and preserves the traditional, per-access atime update semantics.

The option is relevant for filesystems that support atime tracking, including common Linux types such as ext2, ext3, ext4, as well as others like Btrfs and XFS. It is specified at mount time either on the command line or in the filesystem table (fstab). For example: /dev/sda1 / ext4 defaults,strictatime 0 1. The explicit option can be combined with other mount options, but its effect is to force an atime update on each read regardless of any relatime or noatime settings that might otherwise apply.

Implications of using strictatime include increased disk I/O and potentially higher wear on solid-state drives, as every file access can trigger a write to update the timestamp. This can affect system performance, especially on workloads with frequent reads to many files. Administrators typically weigh the need for strict atime semantics against the performance and wear considerations, and may enable strictatime only on systems or directories where applications rely on up-to-date atime values.

In summary, strictatime guarantees per-access atime updates, suitable for applications requiring strict POSIX-like access timestamps, but at the cost of additional I/O and potential performance impact.