fallocate: fallocate failed: Text file busy in ubuntu OS
swapoff -a turns off swap usage. You were trying to allocate 15G to /swapfile,
but you can’t do that if it’s in use.
You do a swapoff -a, fallocate (you may have to delete the current /swapfile first), mkswap /swapfile, then swapon -a.
sudo fallocate -l 1G /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile