Default mount option: relatime vs. noatime

This is not a particularly pressing issue, more something I’ve been wondering about.

Fstab mentions that:

rootfs is not mounted in fstab as we do it via initramfs. Uncomment for remount (slower boot)

while also having the line include noatime should the user decide to uncomment. However the default is the root partition being mounted with relatime.

Is there a reason for this, and would there be any downsides to remounting with noatime & nodiratime after booting has finished?

Thank you in advance.

I would not recommend using noatime. I can’t see much of a benefit from it.

noatime was used when relatime didn’t exist as workaround. Now - use relatime.

Would there be any negative effects though?

If not, I would prefer it over relatime since no application I know of uses the access times. Easy way to reduce unnecessary writes on internal and external storage.

The Posix standard is pretty stupid here. It wants that every access to a file be timestamped.
Means, that everytime you read a file (a process reads a file), the system will write down the last access time of that file. Actually - quite stupid IMHO especially if you have loads of file accesses on a system. If you disable the atime, it will reduce I/O considerably and speed up the system. But not always is it wyse to actually use it - read below:

here a good explanation of the net:
relatime exists as a compromise to ensure that some (older) applications, such as e-mail systems, that use the atime value to determine if a file/message has been read since delivery. As such it is a safe option for a filesystem default.

Before considering mounting a filesystem with noatime you should audit the usage of the filesystem to ensure that no applications depend on atime for correct operation.

The number of writes saved using noatime vs. relatime is miniscule. relatime updates the access time if the file is modified, and mtime is always updated on modify. So, that’s zero additional writes (the times for a single file are always stored in the same disk sector).

The only time you get an additional write from relatime is when the old atime is at least a day ago. So, at most, you get one more disk write per day for files that never change.