Re: df

[Bob Proulx]

Frédéric Robinet wrote:
> after a df on my Debian, I have this:
> 
> Venus:/recup# df -h
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1              15G  610M   14G   5% /
> /dev/sdb1              68G  3.5G   61G   6% /var2
> Venus:/recup#
> 
> 68G - 3.5G = 61G ???

When the filesystem is created 5%-10% of the total disk space will be
reserved by the filesystem as 'minfree'.  This is available only to
root processes and not to non-root processes.  The amount of minfree
is dependent upon the defaults of the particular mkfs.  You probably
have 5% unless you changed it.  Also some disk space will be used by
Inodes in some filesystems.  On others it is dynamic.

  68G - minfree - inodes - 3.5G = 61G

The df program is reporting the numbers as returned from statfs(2).
It is not calculating them as you are doing here.

  man 2 statfs

              struct statfs {
                 long    f_type;     /* type of filesystem (see below) */
                 long    f_bsize;    /* optimal transfer block size */
                 long    f_blocks;   /* total data blocks in file system */
                 long    f_bfree;    /* free blocks in fs */
                 long    f_bavail;   /* free blocks avail to non-superuser */
                 long    f_files;    /* total file nodes in file system */
                 long    f_ffree;    /* free file nodes in fs */
                 fsid_t  f_fsid;     /* file system id */
                 long    f_namelen;  /* maximum length of filenames */
                 long    f_spare[6]; /* spare for later */
              };

Hope that helps,

Bob