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Thread: shred didn't shred

  1. #1
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    shred didn't shred

    System is 64bit 12.04 Ubuntu. I recently used shred to get rid of several files, after which I ran photorec to see how the shredding fared. To my surprise, photorec recovered quite a few of the files I presumed were shredded. More may have been recoverable, but I stopped the process midstream. I used the following command: "shred -u -z -n15 [file name]", which I thought was overkill, but went for it anyway. Any ideas why the files persist?
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  2. #2
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    Re: shred didn't shred

    Shred is not useful on modern journaled file systems. Encrypt your data,then when you need to delete it, hit yourself upside the head with brick to forget the password.

  3. #3
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    Talking Re: shred didn't shred

    Quote Originally Posted by HermanAB View Post
    hit yourself upside the head with brick to forget the password.
    LOL that's a painful way to shred a file!
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  4. #4
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    Re: shred didn't shred

    Quote Originally Posted by Matt 6:27 View Post
    System is 64bit 12.04 Ubuntu. I recently used shred to get rid of several files, after which I ran photorec to see how the shredding fared. To my surprise, photorec recovered quite a few of the files I presumed were shredded. More may have been recoverable, but I stopped the process midstream. I used the following command: "shred -u -z -n15 [file name]", which I thought was overkill, but went for it anyway. Any ideas why the files persist?
    Did you reboot before trying photorec? I'd be interested to see the difference.
    Last edited by philinux; October 29th, 2012 at 08:21 PM.

  5. #5
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    Re: shred didn't shred

    What kind of files were these? And had you previously edited or changed them?

    Just thinking that several applications save the previous version of the file when you make changes. For example if you use gEdit to change an existing file called "test.txt" you will end up with both a "test.txt" and a "test.txt~" file. The latter will not be displayed by Nautilus unless you show hidden files. So maybe you shredded the current version, leaving the former behind - which is what photorec is recovering.

  6. #6
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    Re: shred didn't shred

    Quote Originally Posted by HermanAB View Post
    Shred is not useful on modern journaled file systems. Encrypt your data,then when you need to delete it, hit yourself upside the head with brick to forget the password.

    Right, I understand the journaled file issue, but read somewhere on the forum that shred will work on ext3 and ext4 file systems. Is that not the case?

    With respect to encrypting my files, that works fine except, as you know, it creates a new .gpg file, but retains the original. If shred can't chew up that original, the encryption and brick method doesn't really add anything... except a bump and a headache.
    Gigabyte GA-M57SLI-S4; AMD X2 5600+; 4GB Mushkin Enhanced DDR2 800; Seagate 250GB 7200.10 (SATA);
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  7. #7
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    Re: shred didn't shred

    Quote Originally Posted by philinux View Post
    Did you reboot before trying photorec? I'd be interested to see the difference.

    Good question, but I did reboot. I ran photorec the morning after shredding. Thx for the thought.
    Gigabyte GA-M57SLI-S4; AMD X2 5600+; 4GB Mushkin Enhanced DDR2 800; Seagate 250GB 7200.10 (SATA);
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  8. #8
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    Re: shred didn't shred

    Quote Originally Posted by cryptotheslow View Post
    What kind of files were these? And had you previously edited or changed them?

    Just thinking that several applications save the previous version of the file when you make changes. For example if you use gEdit to change an existing file called "test.txt" you will end up with both a "test.txt" and a "test.txt~" file. The latter will not be displayed by Nautilus unless you show hidden files. So maybe you shredded the current version, leaving the former behind - which is what photorec is recovering.

    Thanks Crypto, good point. File types ranged from open office docs to pics.

    I wasn't targeting a specific file or type, just testing both shred and photorec. There may come a time when I want to shred something and be comfortable it is truly unrecoverable. Based on this preliminary test, I'm not there yet.
    Gigabyte GA-M57SLI-S4; AMD X2 5600+; 4GB Mushkin Enhanced DDR2 800; Seagate 250GB 7200.10 (SATA);
    ASUS DVD-E616A3T (SATA); Samsung SH-S182M (PATA); EVGA GT 220 (all work ootb)

  9. #9
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    Re: shred didn't shred

    Code:
    df -hT
    output please.
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  10. #10
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    Re: shred didn't shred

    Quote Originally Posted by Habitual View Post
    Code:
    df -hT
    output please.
    Code:
    matt6-27:~$ df -hT
    Filesystem     Type      Size  Used Avail Use% Mounted on
    /dev/sde1      ext4      228G   12G  205G   6% /
    udev           devtmpfs  994M  4.0K  994M   1% /dev
    tmpfs          tmpfs     401M  1.2M  400M   1% /run
    none           tmpfs     5.0M     0  5.0M   0% /run/lock
    none           tmpfs    1002M  728K 1002M   1% /run/shm
    Gigabyte GA-M57SLI-S4; AMD X2 5600+; 4GB Mushkin Enhanced DDR2 800; Seagate 250GB 7200.10 (SATA);
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