Defaultsnoatime

Defaultsnoatime is not a single mount option. It typically refers to using the standard default mount options for a filesystem while additionally disabling the updating of access times on reads. In practice, this is written as a comma-separated list in mount options, for example: defaults,noatime. The correct form is to combine options rather than a single token named defaultsnoatime.

Noatime is a mount option that prevents the filesystem from updating the access time (atime) of files when they are read. This reduces the number of write operations, which can improve performance and extend the lifespan of SSDs on servers or systems with heavy I/O. The defaults option is a shorthand that enables a baseline set of common behaviors, including read-write access and other typical permissions. Together, defaults,noatime applies the usual defaults but with atime updates disabled.

Caveats and considerations include compatibility and use-case suitability. Some software relies on atime to detect recently accessed files, and disabling atime can cause unexpected behavior in certain backup tools, file indexing, or scripts that depend on access times. Modern Linux kernels often use relatime by default, which updates atime only when the file’s content has been modified since the last access, offering a compromise between performance and functionality. Using noatime is more aggressive and can break reliance on atime for some workflows. If only directory atimes need to be avoided, nodiratime can be added alongside noatime.

Common usage appears in /etc/fstab lines such as: /dev/sdb1 / ext4 defaults,noatime 0 1. The exact options can vary by filesystem type (ext4, xfs, btrfs) and distribution, but the general principle remains: reduce atime writes by combining defaults with noatime.