[root@centos vagrant]# docker run -ti ubuntu:12.04
Unable to find image 'ubuntu:12.04' locally
Pulling repository ubuntu
78cef618c77e: Download complete
b5da78899d3a: Download complete
87183ecb6716: Download complete
82ed8e312318: Download complete
root@afade8b94d32:/# useradd -m -d /home/dockerinpractice dockerinpractice
root@afade8b94d32:/# echo $?
12
