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Old 01-16-2003, 08:01 AM   #1
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bits and bytes and files basics question

I'm having some trouble with the basics:

cat > touchtext.txt

This creates a files with 1 byte - the letter 'a' with no CR (which would add a byte). This is confirmed by:

ls -l touchtext.txt
-rw-r--r-- 1 root root 1 Jan 16 13:28 touchtext.txt

OK. This is the size of the contents of the file. Now, I can see how much space on the disk this takes:

du -h touchtext.txt
4.0K touchtext.txt

If I make a sentence in the touchtext.txt file like 'Let's vanquish the world of this filthy DMCA trash! Get rid of this trash ... ' then the disk usage is still 4.0K. Not a problem, it's an estimate and it's the size on disk.

2 questions:

1. I'd like to see how much information is taken by storing the additional permissions and timestamp information.
Permissions should be 2 bytes (actually 12 bits?), owner 2 bytes (12 bits?), group 2 bytes (12 bits?), timestamp and name err .. a few bytes each. How can I see this information?

2. If my cluster size is 1024 bytes, why is the size on the disk (although it is only an estimate with du) need 4K?

Any ideas anyone. I'd really appreciate information on the first question especially.

Thanks for any help

PS. I put the questions in bold for people who don't need the explanations.

Last edited by Bert; 01-16-2003 at 08:18 AM.
Old 01-16-2003, 08:28 AM   #2
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du reports disk usage not filesize. It uses the block (or fragment) size of the disk which you can find (as root) with tune2fs -l <dev>. If du <file> reports 4 for a 1 byte file, the minimum allocation size for that partition is 4096, or 4k.

The additional information taken by storing the permissions and timestamp does not take up anymore information. It is stored in the inodes, which are pre-allocated at disk format. Each file takes one inode. Again, tune2fs -l <dev> will give you the total number of inodes on a drive and the number still available.

Chris Winne
Old 01-16-2003, 08:50 AM   #3
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Thanks Chris, yeah I figured that out soon after that this information is not stored against the file but in the inodes, but how can I see the amount of space that inode takes (which will vary for each file), however I also see that tune2fs -l /dev/hdan gives the inode size - 128 bytes. I can work back from there (and that looks to be about right too ) - thanks!

Although my fragment (and block) size is 1024, the allocation size must be 4096 bytes, yes. I was under the impression that the block size is the allocation size *tsk*.



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