Thank you very much for the help.  After I got back the 15GB, I went to my Windows 11 installation and shrunk that volume to get additional space of 300GB (using Disk Management in W11).  Then after a lot of head scratching on how to append this to root partition, someone on AskUbuntu had suggested using Gparted from a bootable USB.  This helped tremendously.  It allowed me to add the 300GB to the root partition and now I have 800GB of space.

I ran Bicoincore last night and voila, I have all the blocks downloaded and syncd.

Thank you everyone for your valuable assistance 

Never mind.  I just realized this is the number of blocks.  Thank you for this tip.  It gave me back 15GB!

Thank you for tips.  I checked the tunefs and got following:

root@simba:~# tune2fs -l /dev/sda4 | grep 'Reserved'
Reserved block count:     6553600
Reserved GDT blocks:      1024
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)

This doesn't seem like 15GB.  Am I correct?

Hello,

I am a newbie.  I installed Ubuntu and ran bitcoind from my user account.  After a little while, I got the following message:

2022-04-23T03:48:14Z *** Disk space is too low!
2022-04-23T03:48:14Z Error: Disk space is too low!
2022-04-23T03:48:14Z FlushStateToDisk: write coins cache to disk (4827382 coins, 685726kB) completed (0.00s)
2022-04-23T03:48:14Z ForceFlushStateToDisk: failed to flush state (Disk space is too low!)
2022-04-23T03:48:14Z FlushStateToDisk: write coins cache to disk (4827382 coins, 685726kB) started
2022-04-23T03:48:14Z *** Disk space is too low!
2022-04-23T03:48:14Z Error: Disk space is too low!
2022-04-23T03:48:14Z FlushStateToDisk: write coins cache to disk (4827382 coins, 685726kB) completed (0.00s)
2022-04-23T03:48:14Z ForceFlushStateToDisk: failed to flush state (Disk space is too low!)
2022-04-23T03:48:15Z Shutdown: done

I allocated 500GB to / during installation.  When I checked the disk space usage, I got the following:

root@simba:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            7.8G     0  7.8G   0% /dev
tmpfs           1.6G  2.0M  1.6G   1% /run
/dev/sda4       492G  467G   90M 100% /
tmpfs           7.8G     0  7.8G   0% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/loop0      249M  249M     0 100% /snap/gnome-3-38-2004/99
/dev/loop1       62M   62M     0 100% /snap/core20/1328
/dev/loop2      128K  128K     0 100% /snap/bare/5
/dev/loop3       66M   66M     0 100% /snap/gtk-common-themes/1519
/dev/loop4       55M   55M     0 100% /snap/snap-store/558
/dev/sda1       256M   90M  167M  36% /boot/efi
tmpfs           1.6G  136K  1.6G   1% /run/user/1000
/dev/loop6      111M  111M     0 100% /snap/core/12834
/dev/loop7      9.0M  9.0M     0 100% /snap/canonical-livepatch/132
/dev/loop8       62M   62M     0 100% /snap/core20/1405
/dev/loop9       44M   44M     0 100% /snap/snapd/15177
/dev/loop10      45M   45M     0 100% /snap/snapd/15534
/dev/loop5      9.0M  9.0M     0 100% /snap/canonical-livepatch/138
root@simba:~#

I am lost as to why so much space is being used by bitcoind.  I would appreciate if someone can shed light on this.