Root partition smaller than partition size

Question

I have Ubuntu installed on VMware. Previous user expanded the size of the partition (I believe by using GParted in boot mode). Now I get warning about free space left on root partition. Unfortunately, it shows everything is 80G except in disk usage tool.

> sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL
NAME                  FSTYPE        SIZE MOUNTPOINT                      LABEL
loop0                 squashfs    132,2M /snap/1password/66              
loop1                 squashfs     83,3M /snap/1password/61              
loop2                 squashfs        4K /snap/bare/5                    
loop3                 squashfs     10,2M /snap/canonical-livepatch/104   
loop4                 squashfs     55,4M /snap/core18/2128               
loop5                 squashfs     10,2M /snap/canonical-livepatch/105   
loop6                 squashfs    208,4M /snap/code/75                   
loop7                 squashfs       13M /snap/dmd/102                   
loop8                 squashfs    216,3M /snap/code/76                   
loop9                 squashfs      219M /snap/gnome-3-34-1804/72        
loop10                squashfs     99,3M /snap/core/11743                
loop11                squashfs     55,5M /snap/core18/2074               
loop12                squashfs      167M /snap/gitkraken/182             
loop13                squashfs      219M /snap/gnome-3-34-1804/66        
loop14                squashfs    162,9M /snap/gnome-3-28-1804/145       
loop15                squashfs     65,2M /snap/gtk-common-themes/1519    
loop16                squashfs     65,1M /snap/gtk-common-themes/1515    
loop17                squashfs    164,8M /snap/gnome-3-28-1804/161       
loop18                squashfs        7M /snap/dub/53                    
loop19                squashfs     32,3M /snap/snapd/13170               
loop20                squashfs    346,9M /snap/wine-platform-runtime/249 
loop21                squashfs    322,8M /snap/wine-platform-6-stable/8  
loop22                squashfs     61,4M /snap/prospect-mail/11          
loop23                squashfs    303,1M /snap/wine-platform-5-stable/16 
loop24                squashfs    126,6M /snap/slack/44                  
loop25                squashfs    303,1M /snap/wine-platform-5-stable/18 
loop26                squashfs       51M /snap/snap-store/547            
loop27                squashfs    168,1M /snap/postman/147               
loop28                squashfs     32,4M /snap/snapd/13270               
loop29                squashfs       51M /snap/snap-store/518            
loop30                squashfs      5,5M /snap/notepad-plus-plus/292     
loop31                squashfs    322,8M /snap/wine-platform-6-stable/5  
loop32                squashfs      5,7M /snap/notepad-plus-plus/307     
loop33                squashfs    127,2M /snap/slack/46                  
loop34                squashfs     99,4M /snap/core/11606                
loop35                squashfs    346,9M /snap/wine-platform-runtime/250 
loop36                squashfs    165,9M /snap/gitkraken/183             
loop37                squashfs    168,1M /snap/postman/148               
loop38                squashfs     64,9M /snap/prospect-mail/16          
sda                                  80G                                 
├─sda1                vfat          512M /boot/efi                       
├─sda2                                1K                                 
├─sda5                ext4          731M /boot                           
└─sda6                crypto_LUKS  78,8G                                 
  └─sda6_crypt        LVM2_member  78,8G                                 
    ├─vgubuntu-root   ext4         77,8G /                               
    └─vgubuntu-swap_1 swap          980M [SWAP]                          
sr0

Answer 1

Looks like your partition is about 80GB but your filesystem is about 30 GB. If you are using ext4, ext3 or ext2 there is a simple way to extend the filesystem using the resize2fs command. You are using LVM so this guide below should solve your problem. You only need to do the resize2fs step but there are a number of other commands there that will help you understand the LVM setup on your machine

https://www.tecmint.com/extend-and-reduce-lvms-in-linux/

Since this is performing significant disk operations you should backup anything you cannot afford to loose.