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I am doing research on Ext4 and I believe I understand the fundamentals of Ext4.

Ext4 stores timestamps. In my assignment, I have proposed to analyse the timestamp of Ext4 MANUALLY instead of typing the command (e.g. date -d @2220775699).

Is there a way to do so?

In addition, why does the timestamp different from the timestamp in the journaling?

Can anyone explain this to me?

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1  
Isn't it just a normal Unix timestamp? –  Alexei Averchenko Aug 7 '13 at 18:23
    
I believe so? I'm analysing it in Ubuntu. –  stupidgal Aug 7 '13 at 18:53
    
What do you mean by "manually"? To me, that means "by hand" which seems to be exactly what you are trying to avoid. –  paddy Aug 8 '13 at 3:31
    
@AlexeiAverchenko: The date command is a standard Unix timestamp, but the Ext4 timestamp isn't. Ext4 supports fractional seconds. –  MSalters Aug 8 '13 at 8:42

2 Answers 2

If you want to translate timestamps to human-friendly description of date and time, then obviously there is a way to do it.

The functions localtime and gmtime are made specifically for this purpose; in glibc, they are implemented in terms of a function __tz_convert, which is implemented in a file tzset.c. You'll probably need to review other functions it uses, though, I haven't studied all of it - GNU source is never easy to read.

UPD: __tz_convert uses __offtime internally.

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Yes, this is possible:

debugfs -R `stat /file/to/check\` /dev/hdX

I'm not sure which two timestamps you're comparing, so I can't explain the difference. (I.e. if you ask a question about a difference, at least tell us between which two things!)

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