findmnt/df discrepancy

findmnt/df discrepancy

[Bruce Dubbs]

I've noticed a discrepancy in percent free between findmnt and df:

$ df -h|grep /tmp
/dev/sdb5        9.8G  8.3G  967M  90% /tmp
$ findmnt --df|grep /tmp
/dev/sdb5  ext4  9.7G  8.3G  967M  85% /tmp

Actually, the discrepancy seems to be df as 8.3/9.8 is 84.7%.
Can anyone here explain the difference?  Should it be submitted to 
coreutils as a bug?

   -- Bruce

Re: findmnt/df discrepancy

[Dave Reisner]

On Wed, Feb 12, 2014 at 09:29:25AM -0600, Bruce Dubbs wrote:
> I've noticed a discrepancy in percent free between findmnt and df:
> 
> $ df -h|grep /tmp
> /dev/sdb5        9.8G  8.3G  967M  90% /tmp
> $ findmnt --df|grep /tmp
> /dev/sdb5  ext4  9.7G  8.3G  967M  85% /tmp
> 
> Actually, the discrepancy seems to be df as 8.3/9.8 is 84.7%.
> Can anyone here explain the difference?  Should it be submitted to
> coreutils as a bug?

It's the reserved space on the filesystem. On an ext4 FS where the
reserved space is 0%, df and findmnt (mostly) agree:

$ df -h | grep Gluttony
 /dev/sdb2             1.8T  701G     1.1T  39% /mnt/Gluttony

$ findmnt --df | grep Gluttony
 /dev/sdb2     ext4    1.8T  700.1G   1.1T  39% /mnt/Gluttony

Re: findmnt/df discrepancy

[Phillip Susi]

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On 02/12/2014 10:38 AM, Dave Reisner wrote:
> It's the reserved space on the filesystem. On an ext4 FS where the 
> reserved space is 0%, df and findmnt (mostly) agree:

Why would findmnt report a different value?  It is the kernel that
adjusts the numbers it returns in statfs(), which both should be using.


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Re: findmnt/df discrepancy

[Karel Zak]

On Fri, Feb 14, 2014 at 11:02:45PM -0500, Phillip Susi wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA512
> 
> On 02/12/2014 10:38 AM, Dave Reisner wrote:
> > It's the reserved space on the filesystem. On an ext4 FS where the 
> > reserved space is 0%, df and findmnt (mostly) agree:
> 
> Why would findmnt report a different value?  It is the kernel that
> adjusts the numbers it returns in statfs(), which both should be using.

I have added a new option --bytes to findmnt(8) (we already have the
same option in lsblk(8)), so now it's more obvious:

        $ df --block-size=1 /dev/sda5
        Filesystem         1B-blocks        Used   Available Use% Mounted on
        /dev/sda5        66650419200 39057010688 24184123392  62% /home

        $ findmnt --df --bytes
        /dev/sda5
        SOURCE    FSTYPE        SIZE        USED       AVAIL USE% TARGET
        /dev/sda5 ext4   66650419200 39057010688 24184123392  59% /home


so yes, both use the same numbers from statvfs(), but findmnt(8)
counts USE% from the USED field, but df(1) counts Use% from the
Available column.

The conversion to human readable sizes is another story:

        $ findmnt --df  /dev/sda5
        SOURCE    FSTYPE  SIZE  USED AVAIL USE% TARGET
        /dev/sda5 ext4   62.1G 36.4G 22.5G  59% /home

        $ df -h /dev/sda5
        master
        Filesystem      Size  Used Avail Use% Mounted on
        /dev/sda5        63G   37G   23G  62% /home


for example available space:

        $ echo "24184123392 / (1024 * 1024 * 1024)" | bc -l
        22.52322006225585937500


    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com