Re: findmnt/df discrepancy

[Karel Zak <kzak@redhat.com>]

On Fri, Feb 14, 2014 at 11:02:45PM -0500, Phillip Susi wrote:
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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.

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