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Since linux 2.6.30, filesystems are mounted with "relatime" by default. In this discussion, Ingo Molnar says he has added the CONFIG_DEFAULT_RELATIME kernel option, which:

makes 'norelatime' the default for all mounts without an extra kernel boot option.

I don't really get it, I wonder if that means that without CONFIG_DEFAULT_RELATIME in .config, a kernel will not use relatime as a default mount option?

How can one enable or disable CONFIG_DEFAULT_RELATIME in make menuconfig? (I don't find anything related to relatime.)

And finally, I can't even find CONFIG_DEFAULT_RELATIME in the kernel sources.

Can someone enlighten me?

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2 Answers 2

up vote 3 down vote accepted

Ingo Molnar proposed a patch, but this patch wasn't accepted into the kernel tree. Linus Torvalds made relatime the default setting in 2.6.30, unconditionally, and this is still true in 3.0. If you want relatime to default off in the kernel, you need to apply Ingo Molnar's patch in your copy of the source.

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ok ! i did not understood the patch wasn't accepted :) –  user368507 Aug 3 '11 at 0:45

If you don't need software that require a FS with atime support, you should go with the mount option "noatime". Relatime is a option for compatibility with atime but without the drawbacks of atime.

If you need support for atime, add "strictatime" to the mount options.

The most important FS in Linux, support the option "noatime". You will gain speed in disk task.

For all mount options "man mount" in your terminal.

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Support for atime is still provided but through the strictatime mount option. atime is no longer considered. Choices are noatime, relatime, or strictatime. –  Stéphane Gimenez Aug 3 '11 at 0:54
    
You're right. The correct option for the traditional "atime" behavior is "strictatime". Thanks. –  Juan Francisco Cantero Hurtado Aug 3 '11 at 1:00
    
Is it recommanded to set strictatime if you plan to do forensic on your linux box ? –  user368507 Aug 3 '11 at 1:01
    
Only if you need to know the last access time to a file. It doesn't show anything important because a application can modify the date without user supervision. –  Juan Francisco Cantero Hurtado Aug 3 '11 at 1:06

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