[cepera@Archlinux ~]$ sudo dd if=/dev/zero of=/swapfile bs=1M count=9000
9000+0 records in
9000+0 records out
9437184000 bytes (9.4 GB, 8.8 GiB) copied, 40.0957 s, 235 MB/s

[cepera@Archlinux ~]$ chmod 600 /swapfile
chmod: changing permissions of '/swapfile': Operation not permitted

[cepera@Archlinux ~]$ sudo chmod 600 /swapfile

[cepera@Archlinux ~]$ sudo mkswap /swapfile
Setting up swapspace version 1, size = 8.8 GiB (9437179904 bytes)
no label, UUID=4963993a-4013-4960-8b86-e3f273cd691f

[cepera@Archlinux ~]$ sudo swapon /swapfile
swapon: /swapfile: swapon failed: Invalid argument

[cepera@Archlinux ~]$ free -h
              total        used        free      shared  buff/cache   available
Mem:          7.7Gi       1.3Gi       128Mi       512Mi       6.2Gi       5.6Gi
Swap:            0B          0B          0B
[cepera@Archlinux ~]$