ForubuntuusersIsuggest[installingdocker](https://docs.docker.com/installation/ubuntulinux/) using docker's own package repository since the version of docker packaged in the ubuntu repositories are a little dated.
Ifyouareusinganolderversionofdocker,youcanusethe[nsenter](http://man7.org/linux/man-pages/man1/nsenter.1.html) linux tool (part of the util-linux package) to access the container shell.