Change "domain.com" with your domain
$ curl -s https://crt.sh/?q=%25.domain.com\&output=json | jq '.[].name_value' | sort -u | sed 's/"//g' | sed '/^*/d'
$ curl -s https://certspotter.com/api/v0/certs\?domain\=domain.com | jq '.[].dns_names[]' | sed 's/\"//g' | sed 's/\*\.//g' | sort -u | grep domain.com
https://www.virustotal.com/gui/domain/domain.com/relations
https://securitytrails.com/list/apex_domain/domain.com
https://github.com/search?q="domain.com"
443.https.tls.certificate.parsed.names: domain.com
https://bgp.he.net/
https://github.com/Edu4rdSHL/findomain
findomain -t domain.com
https://github.com/OWASP/Amass
$ amass enum -d domain.com
https://github.com/subfinder/subfinder
$ ./subfinder -d domain.com -b -w jhaddix_all.txt -t 100
jhaddix all.txt: https://gist.github.com/jhaddix/86a06c5dc309d08580a018c66354a056
$ cat file1 file2 file3 | sort -u | tee uniqSubdomains