Easiest total disk storage usage

It sounds like you're already on the right track. Using the df command with "-h" can display the output in a human readable format. If you apply the "-a" flag, that will display all file systems as well as disk and memory usage.

df -a

Filesystem     1K-blocks    Used Available Use% Mounted on
sysfs                  0       0         0    - /sys
proc                   0       0         0    - /proc
udev              472736       0    472736   0% /dev
devpts                 0       0         0    - /dev/pts
tmpfs             100888    5796     95092   6% /run
/dev/sda        25230876 2451880  21478120  11% /
securityfs             0       0         0    - /sys/kernel/security
tmpfs             504428       0    504428   0% /dev/shm
tmpfs               5120       0      5120   0% /run/lock
tmpfs             504428       0    504428   0% /sys/fs/cgroup

To get an output displaying your disk partitions and usage, you can try the "pydf" command.

pydf

Filesystem Size  Used Avail  Use%                          Mounted on
/dev/sda    24G 2394M   20G   9.7 [##....................] /
/dev/loop0  55M   55M     0 100.0 [######################] /snap/core18/1074
/dev/loop4  55M   55M     0 100.0 [######################] /snap/core18/1098
/dev/loop3  55M   55M     0 100.0 [######################] /snap/core18/1144
/dev/loop1  10M   10M     0 100.0 [######################] /snap/linode-cli/26
/dev/loop2  10M   10M     0 100.0 [######################] /snap/linode-cli/28

Similarly, the "lsblk" command will show your disk in terms of the storage blocks, including your swap image.

lsblk

NAME  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0   7:0    0 54.4M  1 loop /snap/core18/1074
loop1   7:1    0  9.5M  1 loop /snap/linode-cli/26
loop2   7:2    0  9.7M  1 loop /snap/linode-cli/28
loop3   7:3    0 54.4M  1 loop /snap/core18/1144
loop4   7:4    0 54.4M  1 loop /snap/core18/1098
sda     8:0    0 24.5G  0 disk /
sdb     8:16   0  512M  0 disk [SWAP]

Finally, the du command will display disk usage of specific files and directories. you can add the -h flag to get a more concise output:

du -h

4.0K    ./.cache
4.0K    ./.gnupg/private-keys-v1.d
8.0K    ./.gnupg
4.0K    ./snap/linode-cli/26
4.0K    ./snap/linode-cli/common
4.0K    ./snap/linode-cli/28
16K    ./snap/linode-cli
20K    ./snap
152K    ./cli-master/lib/Linode/CLI/Object
196K    ./cli-master/lib/Linode/CLI
232K    ./cli-master/lib/Linode
24K    ./cli-master/lib/WebService/Linode
52K    ./cli-master/lib/WebService
288K    ./cli-master/lib
456K    ./cli-master
572K    .

There are many commands and flags that can be run to understand your disk in terms of space and usage, but these are a great start. If you'd like to learn more, I'd recommend reviewing some online linux resources like Tecmint.com. Good Luck!