thufir@doge:~$
thufir@doge:~$ cat .aws/config
[default]
output = text
region = us-west-2



[profile thufir]
role_arn = arn:aws:iam::1234567890:user/thufir
source_profile = default

thufir@doge:~$
thufir@doge:~$ aws iam list-users
USERS	arn:aws:iam::1234567890:user/thufir	2017-01-02T10:09:01Z	/	ABCDEFGIJKL	thufir
thufir@doge:~$
thufir@doge:~$ aws s3 ls --profile thufir

An error occurred (AccessDenied) when calling the AssumeRole operation: Roles may not be assumed by root accounts.
thufir@doge:~$
thufir@doge:~$ export AWS_DEFAULT_PROFILE=thufir
thufir@doge:~$
thufir@doge:~$ aws s3 ls --profile thufir

An error occurred (AccessDenied) when calling the AssumeRole operation: Roles may not be assumed by root accounts.
thufir@doge:~$