$ cp variables.json.tmpl variables.json
$ vim variables.json
$ packer build -var-file variables.json ubuntu-20.04.json
Default credentials: ubuntu:ubuntu
Change user password in http_ubuntu2004/preseed.cfg :
$ mkpasswd -m sha-512
$ vim http_ubuntu2004/user-data
Default credentials : debian:debian
Change root and user password in http_debian10/preseed.cfg :
$ mkpasswd -m sha-512
$ vim http_debian10/preseed.cfg
Check http/user-data for incorrect interface name.