Why is there a large difference between disk use reported by system information and lsblk and reported by df / du?

Question

When I start a terminal, I see this:

Welcome to Ubuntu 20.04.6 LTS (GNU/Linux 5.4.0-165-generic x86_64)
...
System information as of jeu 26 oct 2023 11:16:34 CEST
System load:            0.45
Usage of /:             49.7% of 455.20GB
Memory usage:           50%
Swap usage:             19%
Processes:              182
Users logged in:        0
=> /bu is using 91.9% of 1.79TB

But when I use du or df, I get:

$ df
Sys. de fichiers            blocs de 1K    Utilisé Disponible Uti% Monté sur
udev                             457888          0     457888   0% /dev
tmpfs                             97128       3040      94088   4% /run
...
/dev/sdc                     1920645740 1765707476   57348560  97% /bu
...
~$ sudo du /bu
4       /bu/lost+found
1765707472      /bu

The results given by du and df (97% used) are identical but very different from the value given by system information (91.9% used). Why is this?

The results (at least in %) are identical for various forms of df:

$ df --si
Sys. de fichiers            Taille Utilisé Dispo Uti% Monté sur
...
/dev/sdc                      2,0T    1,9T   59G  97% /bu
$ df -H
Sys. de fichiers            Taille Utilisé Dispo Uti% Monté sur
...
/dev/sdc                      2,0T    1,9T   59G  97% /bu
~$ df -h
Sys. de fichiers            Taille Utilisé Dispo Uti% Monté sur
...
/dev/sdc                      1,8T    1,7T   55G  97% /bu

------ Edit - Results of lsbk ---- As askeh by Hannu, here is the output. This time, FSUSE% is at 92%, conform to motd. So, it seems the content of the 'MOTD' is based on some extraction of lsblkid. I updated the question title accordingly.

 lsblk -ap -o +MOUNTPOINT,FSTYPE,LABEL,PARTLABEL,FSUSE%,STATE,MODEL
NAME                     MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT     MOUNTPOINT     FSTYPE      LABEL                         PARTLABEL FSUSE% STATE   MODEL
/dev/loop0                 7:0    0         0 loop
...
/dev/loop7                 7:7    0         0 loop
/dev/sda                   8:0    0 465,8G  0 disk                                                                                          running WDC_WD5003ABYX-18WERA0
├─/dev/sda1                8:1    0   243M  0 part /boot          /boot          ext2                                                   60%
├─/dev/sda2                8:2    0     1K  0 part
└─/dev/sda5                8:5    0 465,5G  0 part                               LVM2_member
  ├─/dev/mapper/servamtex2-root
  │                      253:0    0 462,7G  0 lvm  /              /              ext4                                                   50% running
  └─/dev/mapper/servamtex2-swap_1
                         253:2    0   2,8G  0 lvm  [SWAP]         [SWAP]         swap                                                       running
/dev/sdb                   8:16   0 465,8G  0 disk                                                                                          running WDC_WD5002ABYS-18B1B0
├─/dev/sdb2                8:18   0     1K  0 part
└─/dev/sdb5                8:21   0 465,5G  0 part                               LVM2_member
  ├─/dev/mapper/servamtex-root
  │                      253:1    0 462,7G  0 lvm  /servamtex-old /servamtex-old ext4                                                   12% running
  └─/dev/mapper/servamtex-swap_1
                         253:3    0   2,8G  0 lvm                                swap                                                       running
/dev/sdc                   8:32   0   1,8T  0 disk /bu            /bu            ext4                                                   92% running ST2000NM0033-9ZM175

------ Edit 2 df used space ----

My question does not relate to interpretation of df results but why is there a discrepancy between MOTD system information and df information. A possible cause is the difference of 5% as pointed out by @muru

Answer 1

The SIZE argument is an integer and optional unit (example: 10K is 10*1024). Units are K,M,G,T,P,E,Z,Y (powers of 1024) or KB,MB,... (powers of 1000). Binary prefixes can be used, too: KiB=K, MiB=M, and so on.

check the options there is -h and -H for read diiferent: -h, --human-readable print sizes in powers of 1024 (e.g., 1023M) -H, --si print sizes in powers of 1000 (e.g., 1.1G)