I ran into an issue once where a new install of Ubuntu wanted to partition my drive to no more than 200GB. From the command terminal run "sudo df -h" to show your diskspace allocations.
Filesystem Size Used Avail Use% Mounted on
tmpfs 381M 2.0M 379M 1% /run
/dev/sda2 292G 54G 224G 20% /
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
/dev/sda1 511M 5.3M 506M 2% /boot/efi
tmpfs 381M 2.4M 379M 1% /run/user/1000
Another issue you may have is that bitcoind may already be running in the background. If so you won't be able to run bitcoin-qt, nor will you be able to start bitcoind from the terminal. Did you set up a systemd file so bitcoind will start on machine startup?
No, I didn't set it up to start on machine startup. I also just checked to see what processes are running, and it's not listed. To be clear, I ran the GUI first right after install. I only tried bitcoind after the GUI crashed.