"missing" disk space question

I have a nominal 500 GB SSD with one ext4 partition which is used for the OS (UM 20.04) and all other files. The partition was created by the install process when the disk was brand new some years ago.

System monitor reports as follows: about 491 GB total, with 368 GB used.


The disks utility reports 123 GB free. SMART data all look OK.

Caja reports the following regarding the root (only) file system. Used = about 190 GB, free/available about 98 GB.

So, it looks to me as if there is about (500 – 190 – 98) = 212 GB being used in an undefined way according to the caja values. If you use the larger amount of free/available space from the disks utility, the amount of undefined space is about 187 GB, surprisingly close to the size of root (/). It seems almost as if / is being mirrored on the ssd.

I am puzzled by the large apparently hidden space, which is not available for me to use. If possible, I would like to make it available. I would love for someone to help me to understand the values. Probably this is all about educating me, so I appreciate your indulgence.

Hey there :slight_smile:

All filesystem will do some reservations for different purposes.
You are on a ext4 partition that is about to reserve 5% of space for /root

123.1 - 98.1 = 25 - the gap between your values
500 × 0.05 = 25 - the 5% of 500 count

I heard that the 5% value can be changed (I never done it and to be honest I prefer not to advise that) and found this link if you need to do it.

Be aware that a filesystem needs this space to work correctly (defragmentation, ....), you can run into performance issues messing there.

Hi and thanks for the information. That certainly explains the difference between "available" and "free."

I won't be going after that small amount of space, but I am still concerned about the undefined (used?) space of about 187 GB that I can't account for..


As I understood, you do not need that undefined data.
Did you try to format the disk in the process of installation? If you did and there are still no changes, I would try to change the size of the partition and format it again.

My recent experience: about month ago, I installed my new 1TB SSD and I decided to keep root and /home on different partitions. I am glad that I went this way. Because a week ago, I tried to make my scanner working + latest update. As a result, I lost my system :smiley: Even the terminal was hanging :smiley:. I re-intalled the system with formatting only my partition for the system. However I kept my /home with the same user name and password. Please do NOT change any sizes of partitions. However, do not forget to mount all of them. By doing this way, I saved a lot of time. Because ALL my settings (including apps’ settings), desktop and icons were at the place. The adding of my apps back was much easy than installing & making all settings from zero. Also all data on my /home and on additional data partition were saved too.

With 500Gb, I would keep around 50Gb for the system, plus /boot/efi , plus swap and rest for your /home. But it is just my opinion.

This is what I have right now: 100Gb for the system and 600Gb for /home

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Thanks snow_dog.

I have been trying to avoid reformatting, but I am afraid that is my last resort. I appreciate the partitioning info.

Oh, BTW, good luck with your scanner. Scanners and printers have been a real pain to me as well.