System load:  0.0               Processes:             104
Usage of /:   91.7% of 3.87GB   Users logged in:       1
Memory usage: 37%               IP address for enp0s3: <removed by me>
Swap usage:   0%

    => / is using 91.7% of 3.87GB

sudo lsblk -o NAME, FSTYPE, SIZE, MOUNTPOINT, LABEL

NAME                      FSTYPE       SIZE MOUNTPOINT            LABEL
loop0                     squashfs    38,7M /snap/postgresql10/47
loop1                     squashfs    86,9M /snap/core/4917
loop2                     squashfs    89,5M /snap/core/6130
loop3                     squashfs    57,1M /snap/powershell/17
loop4                     squashfs    57,1M /snap/powershell/14
sda                                     25G
├─sda1                                   1M
├─sda2                    ext4           1G /boot
└─sda3                    LVM2_member   24G
  └─ubuntu--vg-ubuntu--lv ext4           4G /
sr0                                   1024M