Tenho o mesmo problema acima. Tenho um HD SSD onde estão instalados o Ubuntu e o Windows e o outros dois HDs para arquivos, e pelo Ubuntu não consigo apagar arquivos dos dois.
Usei o comando indicado e obtive o seguinte resultado:
NAME FSTYPE LABEL UUID FSAVAIL FSUSE% MOUNTPOINT SIZE OWNER GROUP MODE
loop0
squash 0 100% /snap/core 96,6M root disk brw-rw----
loop1
squash 0 100% /snap/core 55,3M root disk brw-rw----
loop2
squash 0 100% /snap/core 55M root disk brw-rw----
loop3
squash 0 100% /snap/core 97,1M root disk brw-rw----
loop4
squash 0 100% /snap/gnom 255,6M root disk brw-rw----
loop5
squash 0 100% /snap/gtk- 54,8M root disk brw-rw----
loop6
squash 0 100% /snap/gnom 255,6M root disk brw-rw----
loop7
squash 0 100% /snap/snap 49,8M root disk brw-rw----
loop8
squash 0 100% /snap/gtk- 62,1M root disk brw-rw----
loop9
squash 0 100% /snap/snap 49,8M root disk brw-rw----
sda 223,6G root disk brw-rw----
├─sda1
│ ntfs Reservado pelo Sistema
│ 1A484ECD484EA6FB 579M root disk brw-rw----
├─sda2
│ ntfs C474556574555B6E 143,9G root disk brw-rw----
├─sda3
│ 1K root disk brw-rw----
└─sda5
ext4 64b95443-1228-4b3e-a431-11bcf887c732 61,7G 15% / 79,2G root disk brw-rw----
sdb 931,5G root disk brw-rw----
├─sdb1
│ ntfs Reservado pelo Sistema
│ 9ED4F4FCD4F4D80B 100M root disk brw-rw----
├─sdb2
│ ntfs CC7079A970799AC2 931G root disk brw-rw----
└─sdb3
ntfs 5A889CEC889CC7C1 450M root disk brw-rw----
sdc 372,6G root disk brw-rw----
└─sdc1
ntfs 4CC40331C4031CB8 78G 79% /media/jon 372,6G root disk brw-rw----
sr0 1024M root cdrom brw-rw----