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Thread: df mystery

  1. #1

    Default df mystery

    Hello,

    I was alarmed to discover that df reports 99% full on my biggest partition, but on closer inspection found that the numbers did not add up:

    Filesystem 1K-blocks Used Available Use% Mounted on
    /dev/sda7 445062208 416628196 5826144 99% /home

    the difference between the total reported space and the reported used space is over 28Gb, but the available space is reported as just under 6Gb.

    Is there any way I can discover what is wrong here, or should I enroll back in primary school and re-learn how to add?

    Thanks,

    Abe

  2. #2
    Join Date
    Jun 2008
    Location
    Kansas City Area, Missouri, USA
    Posts
    7,236

    Default Re: df mystery

    naimab wrote:
    > Hello,
    >
    > I was alarmed to discover that df reports 99% full on my biggest
    > partition, but on closer inspection found that the numbers did not add
    > up:
    >
    > Filesystem 1K-blocks Used Available Use% Mounted on
    > /dev/sda7 445062208 416628196 5826144 99% /home
    >
    > the difference between the total reported space and the reported used
    > space is over 28Gb, but the available space is reported as just under
    > 6Gb.
    >
    > Is there any way I can discover what is wrong here, or should I enroll
    > back in primary school and re-learn how to add?


    No, your math is OK. When an ext3 partition is created using the
    defaults, a certain percentage is reserved for use by root, which is
    your 28 GB. Such reservation is to allow Linux to boot even if all the
    user space is allocated, and is a safety measure.

  3. #3
    Join Date
    Jun 2008
    Location
    Netherlands
    Posts
    29,769

    Default Re: df mystery

    Adding to the excelent expllanation of lwfinger, the default reserved space in ext2/3 is 5%. Now on todays very big file systems this can lead to a large amount (in your case more then 20GB). You can change this (live) using
    Code:
    tune2fs -m ...
    see the man page of tune2fs. My opinion is not to put it to 0%, but some people might argue that that is not a problem on data only file systems (like containing a database) because boot does not use something there.
    Henk van Velden

  4. #4

    Default Re: df mystery

    Many thanks for both the explanation and the advice. It was a surprise to learn from you that even on a non-bootable partition so much space is reserved for root, but the good news is that apparently I can add numbers up

    It is reasonable to assume that root will not need so much space, so I think I will reduce it to less than 1% - this is a data only partition after all.

    Thanks again,

    Abe

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