AWS EC2 default user name for the AMI that you used to launch your instance

For Amazon Linux 2 or the Amazon Linux AMI, the user name is ec2-user.

For a Centos AMI, the user name is centos.

For a Debian AMI, the user name is admin or root.

For a Fedora AMI, the user name is ec2-user or fedora.

For a RHEL AMI, the user name is ec2-user or root.

For a SUSE AMI, the user name is ec2-user or root.

For an Ubuntu AMI, the user name is ubuntu.

Otherwise, if ec2-user and root don't work, check with the AMI provider.