Hi,

I've tried the recommendation of using either cloud-boothook or bootcmd to move fallocate under /root but I dont see cloud-init to fallback to dd to create a swap image

```bash
[root@ArchLinux ~]# grep -Ei swap /var/log/cloud-init*
/var/log/cloud-init-output.log:2020-09-23 21:59:21,516 - cc_mounts.py[WARNING]: Failed to create swapfile '/swapfile' of size 2048MB via fallocate: Unexpected error while running command.
/var/log/cloud-init-output.log:Command: ['fallocate', '-l', '2048M', '/swapfile']
/var/log/cloud-init-output.log:2020-09-23 21:59:21,530 - cc_mounts.py[WARNING]: failed to setup swap: [Errno 2] No such file or directory: '/swapfile'
/var/log/cloud-init.log:2020-09-23 21:59:21,508 - cc_mounts.py[DEBUG]: Attempting to determine the real name of swap
/var/log/cloud-init.log:2020-09-23 21:59:21,508 - cc_mounts.py[DEBUG]: changed default device swap => None
/var/log/cloud-init.log:2020-09-23 21:59:21,508 - cc_mounts.py[DEBUG]: Ignoring nonexistent default named mount swap
/var/log/cloud-init.log:2020-09-23 21:59:21,509 - cc_mounts.py[DEBUG]: suggest 2048.0 MB swap for 1983.95703125 MB memory with '9028.85546875 MB' disk given max=2048.0 MB [max=2048.0 MB]'
/var/log/cloud-init.log:2020-09-23 21:59:21,509 - cc_mounts.py[DEBUG]: Creating swapfile in '/swapfile' on fstype 'ext4' using 'fallocate'
/var/log/cloud-init.log:2020-09-23 21:59:21,509 - util.py[DEBUG]: Running command ['fallocate', '-l', '2048M', '/swapfile'] with allowed return codes [0] (shell=False, capture=True)
/var/log/cloud-init.log:2020-09-23 21:59:21,516 - cc_mounts.py[WARNING]: Failed to create swapfile '/swapfile' of size 2048MB via fallocate: Unexpected error while running command.
/var/log/cloud-init.log:Command: ['fallocate', '-l', '2048M', '/swapfile']
/var/log/cloud-init.log:2020-09-23 21:59:21,529 - util.py[DEBUG]: Attempting to remove /swapfile
/var/log/cloud-init.log:2020-09-23 21:59:21,530 - util.py[DEBUG]: Setting up swap file took 0.022 seconds
/var/log/cloud-init.log:2020-09-23 21:59:21,530 - cc_mounts.py[WARNING]: failed to setup swap: [Errno 2] No such file or directory: '/swapfile'
 ```

although I see in code an exception 

https://github.com/canonical/cloud-init/blob/master/cloudinit/config/cc_mounts.py#L270

Any ideas ?

thanks in advance