To atime or relatime?
Joe Nall
joe at nall.com
Thu Jun 14 10:27:32 UTC 2012
On Jun 13, 2012, at 11:53 PM, Shawn Wells wrote:
> I received this note from a colleague today regarding content in the scap-security-guide for RHEL6:
>
>> Ext4 mounts devices with the relatime option by default. Probably not a good idea for secure environments. Means atime is not accurate. Very bad for systems using AIDE. RHEL 6 security guide needs to turn atime back on for Ext4 mounts.
>>
>> cat /proc/mounts
>>
>> Sent from iPhone.
>>
>
> When he states that "atime is not accurate" I believe he's referring to how relatime maintains atime data, but not for each time the file was accessed. Only modified.
>
> From a performance perspective relatime makes a lot of sense. Enablement of relatime means that the filesystem will not write read-times to a file when read. Imagine recording every time a file in hadoop or a highly utilized fileshare was read... that could be a lot of overhead which relatime prevents.
>
> With that said, we're writing a security guide and not a performance guide. What does everyone think about this, and what should we do? One option is to set "default_relatime=0" in grub to prevent any filesystem from doing this. Is that overkill?
Overkill
Audit rules record when something you care about has been accessed.
joe
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